diff --git a/handbook/hw.sgml b/handbook/hw.sgml index a2dc179405..e67e8bdf68 100644 --- a/handbook/hw.sgml +++ b/handbook/hw.sgml @@ -1,1510 +1,1531 @@ - + PC Hardware compatibility

Issues of hardware compatibility are among the most troublesome in the computer industry today and FreeBSD is by no means immune to trouble. In this respect, FreeBSD's advantage of being able to run on inexpensive commodity PC hardware is also its liability when it comes to support for the amazing variety of components on the market. While it would be impossible to provide a exhaustive listing of hardware that FreeBSD supports, this section serves as a catalog of the device drivers included with FreeBSD and the hardware each drivers supports. Where possible and appropriate, notes about specific products are included. As FreeBSD is a volunteer project without a funded testing department, we depend on you, the user, for much of the information contained in this catalog. If you have direct experience of hardware that does or does not work with FreeBSD, please let us know by sending e-mail to the &a.doc;. Questions about supported hardware should be directed to the &a.questions (see for more information). When submitting information or asking a question, please remember to specify exactly what version of FreeBSD you are using and include as many details of your hardware as possible. Resources on the Internet

The following links have proven useful in selecting hardware. Though some of what you see won't necessarily be specific (or even applicable) to FreeBSD, most of the hardware information out there is OS independent. Please check with the FreeBSD hardware guide to make sure that your chosen configuration is supported before making any purchases.

Sample Configurations

The following list of sample hardware configurations by no means constitutes an endorsement of a given hardware vendor or product by The FreeBSD Project. This information is provided only as a public service and merely catalogs some of the experiences that various individuals have had with different hardware combinations. Your mileage may vary. Slippery when wet. Beware of dog. - Jordan's Picks + Jordan's Picks

I have had fairly good luck building workstation and server configurations with the following components. I can't guarantee that you will too, nor that any of the companies here will remain "best buys" forever. I will try, when I can, to keep this list up-to-date but cannot obviously guarantee that it will be at any given time. Motherboards

The motherboard appears to be a good choice for mid-to-high range Pentium server and workstation systems. You might also wish to investigate ASUS's offering if it's a 486-class motherboard you're looking for (Note: These have become increasingly hard to get as ASUS apparently no longer manufactures them). Those wishing to build more fault-tolerant systems should also be sure to use Parity memory or, for truly 24/7 applications, ECC memory. Note that ECC memory does involve a slight performance trade-off (which may or may not be noticable depending on your application) but buys you significantly increased fault-tolerance to memory errors.

At the higher end, the Intel/Venus Pro () motherboard appears to work very well with FreeBSD, as does its accompanying 200Mhz P6 (Pentium Pro) CPU. Recent price drops have dropped P6 systems into a very affordable price bracket, at least in the United States, and for serious server applications you may wish to look no further than the Pentium Pro. My personal `make world' times dropped from 3 hours and 40 minutes with a P5/166 to 1 hour and 22 minutes when I upgraded to a P6/200 machine - not a fair comparison, to be sure, but just to note that in terms of increased productivity, the P6/200 has definitely been worth the upgrade for me. NOTE: The Intel motherboards are designed to a different form-factor and hence require an entirely different PC case, the so-called "ATX" case design. Consider this fact carefully if you're thinking of upgrading an existing system - all the commonly available ATX cases I've seen so far have been in the "midi-tower" class, with limited space for drives or other internal peripherals available. On the plus side, most ATX cases appear to be of much higher quality than their typical PC counterparts. The only known interoperability problem with the chipset (also known as ``Natoma'') is that the Matrox Meteor frame-grabber board will lock up your system if used in one of these motherboards. Matrox blames Intel, Intel blames Matrox, all we know is that it definitely doesn't work. That is the only card I've had any troubles with in my P6 system and the card works just fine in my older Triton chipset based motherboard. Disk Controllers

This one is a bit trickier, and while I used to recommend the controllers unilaterally for everything from ISA to PCI, now I tend to lean towards the 1542CF for ISA, Buslogic Bt747c for EISA and Adaptec 2940 for PCI. The NCR/Symbios cards for PCI have also worked well for me, though you need to make sure that your motherboard supports the BIOS-less model if you're using one of those (if your card has nothing which looks even vaguely like a ROM chip on it, you've probably got one which expects its BIOS to be on your motherboard).

If you should find that you need more than one SCSI controller in a PCI machine, you may wish to consider conserving your scarce PCI bus resources by buying the Adaptec 3940 card, which puts two SCSI controllers (and internal busses) in a single slot. Disk drives

In this particular game of Russian roulette, I'll make few specific recommendations except to say "SCSI over IDE whenever you can afford it." Even in small desktop configurations, SCSI often makes more sense since it allows you to easily migrate drives from server to desktop as falling drive prices make it economical to do so. If you have more than one machine to administer then think of it not simply as storage, think of it as a food chain!

I do not currently see SCSI WIDE drives as a necessary expense unless you're putting together an NFS or NEWS server that will be doing a lot of multiuser disk I/O. - CDROM drives + CDROM drives

My SCSI preferences extend to SCSI CDROM drives as well, and while the XM-3501B (also released in a caddy-less model called the XM-5401B) drive has always performed well for me, I'm now a great fan of the PX-12CS drive. It's a 12 speed drive with excellent performance and reliability.

Generally speaking, most SCSI CDROM drives I've seen have been of pretty solid construction and you probably won't go wrong with an HP or NEC SCSI CDROM drive either. SCSI CDROM prices also appear to have dropped considerably in the last few months and are now quite competitive with IDE CDROMs while remaining a technically superior solution. I now see no reason whatsoever to settle for an IDE CDROM drive if given a choice between the two. CD Recordable (WORM) drives

At the time of this writing, FreeBSD supports 3 types of CDR drives (though I believe they all ultimately come from Phillips anyway): The Phillips CDD 522 (Acts like a Plasmon), the PLASMON RF4100 and the HP 4020i. I myself use the HP 4020i for burning CDROMs (with 2.2-current - it does not work with 2.1.5 or earlier releases of the SCSI code) and it works very well. See on your 2.2 system for example scripts used to created ISO9660 filesystem images (with RockRidge extensions) and burn them onto an HP4020i CDR. Tape drives

I've had pretty good luck with both from and drives from .

For backup purposes, I'd have to give the higher recommendation to the Exabyte due to the more robust nature (and higher storage capacity) of 8mm tape. Video Cards

If you can also afford to buy a commercial X server for US$99 from then I can heartily recommend the card. Note that support for this card is also getting better with the server, which is available free of charge, though it's still a fair bit slower than the XiG product at this time. I'm told that support is also a fair bit better in the 3.2A release of XFree86, but it's not yet available for general release. You also certainly can't go wrong with one of cards - their S3 Vision 868 and 968 based cards (the 9FX series) also being quite fast and very well supported by XFree86's S3 server. Monitors

I have had very good luck with the , as have I with the Viewsonic offering in the same (trinitron) tube. For larger than 17", all I can recommend at the time of this writing is to not spend any less than U.S. $2,500 for a 21" monitor if that's what you really need. There are good monitors available in the >=20" range and there are also cheap monitors in the >=20" range. Unfortunately, very few are both cheap and good! Networking

I can recommend the Ultra 16 controller for any ISA application and the SMC EtherPower or Compex ENET32 cards for any serious PCI based networking. Both of the PCI cards are based around DEC's DC21041 Ethernet controller chip and other cards using it, such as the Zynx ZX342 or DEC DE435, will generally work as well. For 100Mbit networking, either the SMC SMC9332DST 10/100MB or Intel EtherExpress Pro/100B cards will do a fine job. If what you're looking for is, on the other hand, the cheapest possible solution which will still work reasonably well, then almost any NE2000 clone is a good choice. Serial

If you're looking for high-speed serial networking solutions, then makes the series, with drivers now in FreeBSD-current. also manufactures a board with T1/E1 capabilities, using software they provide. I have no direct experience using either product, however.

Multiport card options are somewhat more numerous, though it has to be said that FreeBSD's support for 's products is probably the tightest, primarily as a result of that company's commitment to making sure that we are adequately supplied with evaluation boards and technical specs. I've heard that the Cyclom-16Ye offers the best price/performance, though I've not checked the prices lately. Other multiport cards I've heard good things about are the BOCA and AST cards, and apparently offers an unofficial driver for their cards at location. Audio

I currently use the Ultrasound MAX due to its high sound quality and full-duplex audio capabilities (dual DMA channels). Support for Windows NT and OS/2 is fairly anemic, however, so I'm not sure that I can recommend it as an all-around card for a machine that will be running both FreeBSD and NT or OS/2. In such a scenario, I might recommend the AWE32 instead. Video

For video capture, there's really only once choice - the card. FreeBSD also supports the older video spigot card from Creative Labs, but those are getting somewhat difficult to find and the Meteor is a more current generation frame-grabber with a higher-speed PCI interface. Note that this card will not work with motherboards based on the VS440FX chipset! See the section for details. Core/Processing Motherboards, busses, and chipsets * ISA * EISA * VLB PCI

Contributed by &a.rgrimes;.25 April 1995.

Continuing updates by &a.jkh;.Last update on 26 August 1996.

Of the Intel PCI chip sets, the following list describes various types of known-brokenness and the degree of breakage, listed from worst to best.

Mercury: Cache coherency problems, especially if there are ISA bus masters behind the ISA to PCI bridge chip. Hardware flaw, only known work around is to turn the cache off. Saturn-I (ie, 82424ZX at rev 0, 1 or 2): Write back cache coherency problems. Hardware flaw, only known work around is to set the external cache to write-through mode. Upgrade to Saturn-II. Saturn-II (ie, 82424ZX at rev 3 or 4): Works fine, but many MB manufactures leave out the external dirty bit SRAM needed for write back operation. Work arounds are either run it in write through mode, or get the dirty bit SRAM installed. (I have these for the ASUS PCI/I-486SP3G rev 1.6 and later boards). Neptune: Can not run more than 2 bus master devices. Admitted Intel design flaw. Workarounds include do not run more than 2 bus masters, special hardware design to replace the PCI bus arbiter (appears on Intel Altair board and several other Intel server group MB's). And of course Intel's official answer, move to the Triton chip set, we ``fixed it there''. Triton: No known cache coherency or bus master problems, chip set does not implement parity checking. Workaround for parity issue. Use Triton-II based motherboards if you have the choice. Triton-II: All reports on motherboards using this chipset have been favorable so far. No known problems. Orion: Early versions of this chipset suffered from a PCI write-posting bug which can cause noticeable performance degradation in applications where large amounts of PCI bus traffic is involved. B0 stepping or later revisions of the chipset fixed this problem. :This support chipset seems to work well, and does not suffer from any of the early Orion chipset problems. It also supports a wider variety of memory, including ECC and parity. The only known problem with it is that the Matrox Meteor frame grabber card doesn't like it.

CPUs/FPUs * Pentium Pro class Pentium class Clock speeds

Contributed by &a.rgrimes;.1 October 1996.

Pentium class machines use different clock speeds for the various parts of the system. These being the speed of the CPU, external memory bus, and the PCI bus. It is not always true that a "faster" processor will make a system faster than a "slower" one, due to the various clock speeds used. Below is a table showing the differences:

Rated External Clock External to PCI Bus CPU and Memory Bus Internal Clock Clock MHZ MHZ** Multiplier MHZ 60 60 1.0 30 66 66 1.0 33 75 50 1.5 25 90 60 1.5 30 100 50* 2 25 100 66 1.5 33 120 60 2 30 133 66 2 33 150 60 2.5 30 166 66 2.5 33 180 60 3 30 200 66 3 33 * The Pentium 100 can be run at either 50MHz external clock with a multiplier of 2 or at 66MHz and a multiplier of 1.5. ** 66 Mhz may actually be 66.667 MHz, but don't assume so.

As can be seen the best parts to be using are the 100, 133, 166 and 200, with the exception that at a mulitplier of 3 the CPU starves for memory. * 486 class * 386 class 286 class

Sorry, FreeBSD does not run on 80286 machines. It is nearly impossible to run today's large full-featured UNIXes on such hardware. * Memory

The mininum amount of memory you must have to install FreeBSD is 5 MB. Once your system is up and running you can that will use less memory. If you use the boot4.flp you can get away with having only 4 MB. * BIOS Input/Output Devices * Video cards * Sound cards Serial ports and multiport cards &uart; &sio; &cy; * Parallel ports * Modems * Network cards * Keyboards * Mice * Other Storage Devices &esdi; &scsi; * Disk/tape controllers * SCSI * IDE * Floppy * Hard drives Tape drives

Contributed by &a.jmb;.2 July 1996.

General tape access commands

mt(1) provides generic access to the tape drives. Some of the more common commands are rewind, erase, and status. See the mt(1) manual page for a detailed description. Controller Interfaces

There are several different interfaces that support tape drives. The interfaces are SCSI, IDE, Floppy and Parallel Port. A wide variety of tape drives are available for these interfaces. Controllers are discussed in SCSI drives

The st(4) driver provides support for 8mm (Exabyte), 4mm (DAT: Digital Audio Tape), QIC (Quarter-Inch Cartridge), DLT (Digital Linear Tape), QIC Minicartridge and 9-track (remember the big reels that you see spinning in Hollywood computer rooms) tape drives. See the st(4) manual page for a detailed description.

The drives listed below are currently being used by members of the FreeBSD community. They are not the only drives that will work with FreeBSD. They just happen to be the ones that we use. 4mm (DAT: Digital Audio Tape)

8mm (Exabyte)

QIC (Quarter-Inch Cartridge)

DLT (Digital Linear Tape)

Mini-Cartridge

Autoloaders/Changers

* IDE drives Floppy drives

* Parallel port drives Detailed Information

The boot message identifier for this drive is "ARCHIVE ANCDA 2750 28077 -003 type 1 removable SCSI 2"

This is a QIC tape drive.

Native capacity is 1.35GB when using QIC-1350 tapes. This drive will read and write QIC-150 (DC6150), QIC-250 (DC6250), and QIC-525 (DC6525) tapes as well.

Data transfer rate is 350kB/s using dump(8). Rates of 530kB/s have been reported when using

Production of this drive has been discontinued.

The SCSI bus connector on this tape drive is reversed from that on most other SCSI devices. Make sure that you have enough SCSI cable to twist the cable one-half turn before and after the Archive Anaconda tape drive, or turn your other SCSI devices upside-down.

Two kernel code changes are required to use this drive. This drive will not work as delivered.

If you have a SCSI-2 controller, short jumper 6. Otherwise, the drive behaves are a SCSI-1 device. When operating as a SCSI-1 device, this drive, "locks" the SCSI bus during some tape operations, including: fsf, rewind, and rewoffl.

If you are using the NCR SCSI controllers, patch the file /usr/src/sys/pci/ncr.c (as shown below). Build and install a new kernel. *** 4831,4835 **** }; ! if (np->latetime>4) { /* ** Although we tried to wake it up, --- 4831,4836 ---- }; ! if (np->latetime>1200) { /* ** Although we tried to wake it up,

Reported by: &a.jmb;

The boot message identifier for this drive is "ARCHIVE Python 28454-XXX4ASB" "type 1 removable SCSI 2" "density code 0x8c, 512-byte blocks"

This is a DDS-1 tape drive.

Native capacity is 2.5GB on 90m tapes.

Data transfer rate is XXX.

This drive was repackaged by Sun Microsystems as model 411.

Reported by: Bob Bishop rb@gid.co.uk

The boot message identifier for this drive is "ARCHIVE VIPER 60 21116 -007" "type 1 removable SCSI 1"

This is a QIC tape drive.

Native capacity is 60MB.

Data transfer rate is XXX.

Production of this drive has been discontinued.

Reported by: Philippe Regnauld regnauld@hsc.fr

The boot message identifier for this drive is "ARCHIVE VIPER 150 21531 -004" "Archive Viper 150 is a known rogue" "type 1 removable SCSI 1". A multitude of firmware revisions exist for this drive. Your drive may report different numbers (e.g "21247 -005".

This is a QIC tape drive.

Native capacity is 150/250MB. Both 150MB (DC6150) and 250MB (DC6250) tapes have the recording format. The 250MB tapes are approximately 67% longer than the 150MB tapes. This drive can read 120MB tapes as well. It can not write 120MB tapes.

Data transfer rate is 100kB/s

This drive reads and writes DC6150 (150MB) and DC6250 (250MB) tapes.

This drives quirks are known and pre-compiled into the scsi tape device driver (st(4)).

Under FreeBSD 2.2-current, use mt blocksize 512 to set the blocksize. (The particular drive had firmware revision 21247 -005. Other firmware revisions may behave differently) Previous versions of FreeBSD did not have this problem.

Production of this drive has been discontinued.

Reported by: Pedro A M Vazquez vazquez@IQM.Unicamp.BR

Mike Smith msmith@atrad.adelaide.edu.au

The boot message identifier for this drive is "ARCHIVE VIPER 2525 25462 -011" "type 1 removable SCSI 1"

This is a QIC tape drive.

Native capacity is 525MB.

Data transfer rate is 180kB/s at 90 inches/sec.

The drive reads QIC-525, QIC-150, QIC-120 and QIC-24 tapes. Writes QIC-525, QIC-150, and QIC-120.

Firmware revisions prior to "25462 -011" are bug ridden and will not function properly.

Production of this drive has been discontinued.

The boot message identifier for this drive is "Conner tape".

This is a floppy controller, minicartridge tape drive.

Native capacity is XXXX

Data transfer rate is XXX

The drive uses QIC-80 tape cartridges.

Reported by: Mark Hannon mark@seeware.DIALix.oz.au

The boot message identifier for this drive is "CONNER CTMS 3200 7.00" "type 1 removable SCSI 2".

This is a minicartridge tape drive.

Native capacity is XXXX

Data transfer rate is XXX

The drive uses QIC-3080 tape cartridges.

Reported by: Thomas S. Traylor tst@titan.cs.mci.com

The boot message identifier for this drive is "DEC TZ87 (C) DEC 9206" "type 1 removable SCSI 2" "density code 0x19"

This is a DLT tape drive.

Native capacity is 10GB.

This drive supports hardware data compression.

Data transfer rate is 1.2MB/s.

This drive is identical to the Quantum DLT2000. The drive firmware can be set to emulate several well-known drives, including an Exabyte 8mm drive.

Reported by: &a.wilko;

The boot message identifier for this drive is "EXABYTE EXB-2501"

This is a mini-cartridge tape drive.

Native capacity is 1GB when using MC3000XL minicartridges.

Data transfer rate is XXX

This drive can read and write DC2300 (550MB), DC2750 (750MB), MC3000 (750MB), and MC3000XL (1GB) minicartridges.

WARNING: This drive does not meet the SCSI-2 specifications. The drive locks up completely in response to a SCSI MODE_SELECT command unless there is a formatted tape in the drive. Before using this drive, set the tape blocksize with mt -f /dev/st0ctl.0 blocksize 1024 Before using a minicartridge for the first time, the minicartridge must be formated. FreeBSD 2.1.0-RELEASE and earlier: /sbin/scsi -f /dev/rst0.ctl -s 600 -c "4 0 0 0 0 0" (Alternatively, fetch a copy of the scsiformat shell script from FreeBSD 2.1.5/2.2.) FreeBSD 2.1.5 and later: /sbin/scsiformat -q -w /dev/rst0.ctl

Right now, this drive cannot really be recommended for FreeBSD.

Reported by: Bob Beaulieu ez@eztravel.com

The boot message identifier for this drive is "EXABYTE EXB-8200 252X" "type 1 removable SCSI 1"

This is an 8mm tape drive.

Native capacity is 2.3GB.

Data transfer rate is 270kB/s.

This drive is fairly slow in responding to the SCSI bus during boot. A custom kernel may be required (set SCSI_DELAY to 10 seconds).

There are a large number of firmware configurations for this drive, some have been customized to a particular vendor's hardware. The firmware can be changed via EPROM replacement.

Production of this drive has been discontinued.

Reported by: Mike Smith msmith@atrad.adelaide.edu.au

The boot message identifier for this drive is "EXABYTE EXB-8500-85Qanx0 0415" "type 1 removable SCSI 2"

This is an 8mm tape drive.

Native capacity is 5GB.

Data transfer rate is 300kB/s.

Reported by: Greg Lehey grog@lemis.de

The boot message identifier for this drive is "EXABYTE EXB-85058SQANXR1 05B0" "type 1 removable SCSI 2"

This is an 8mm tape drive which supports compression, and is upward compatible with the EXB-5200 and EXB-8500.

Native capacity is 5GB.

The drive supports hardware data compression.

Data transfer rate is 300kB/s.

Reported by: Glen Foster gfoster@gfoster.com

The boot message identifier for this drive is "HP C1533A 9503" "type 1 removable SCSI 2".

This is a DDS-2 tape drive. DDS-2 means hardware data compression and narrower tracks for increased data capacity.

Native capacity is 4GB when using 120m tapes. This drive supports hardware data compression.

Data transfer rate is 510kB/s.

This drive is used in Hewlett-Packard's SureStore 6000eU and 6000i tape drives and C1533A DDS-2 DAT drive.

The drive has a block of 8 dip switches. The proper settings for FreeBSD are: 1 ON; 2 ON; 3 OFF; 4 ON; 5 ON; 6 ON; 7 ON; 8 ON. switch 1 2 Result ON ON Compression enabled at power-on, with host control ON OFF Compression enabled at power-on, no host control OFF ON Compression disabled at power-on; the host is allowed to control compression OFF OFF Compression disabled at power-on, no host control

Switch 3 controls MRS (Media Recognition System). MRS tapes have stripes on the transparent leader. These identify the tape as DDS (Digital Data Storage) grade media. Tapes that do not have the stripes will be treated as write-protected. Switch 3 OFF enables MRS. Switch 3 ON disables MRS.

See and for more information on configuring this drive.

Warning: Quality control on these drives varies greatly. One FreeBSD core-team member has returned 2 of these drives. Neither lasted more than 5 months.

Reported by: &a.se;

The boot message identifier for this drive is "HP HP35470A T503" type 1 removable SCSI 2" "Sequential-Access density code 0x13, variable blocks".

This is a DDS-1 tape drive. DDS-1 is the original DAT tape format.

Native capacity is 2GB when using 90m tapes.

Data transfer rate is 183kB/s.

The same mechanism is used in Hewlett-Packard's SureStore tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT drive and HP C1536A DDS format DAT drive.

The HP C1534A DDS format DAT drive has two indicator lights, one green and one amber. The green one indicates tape action: slow flash during load, steady when loaded, fast flash during read/write operations. The amber one indicates warnings: slow flash when cleaning is required or tape is nearing the end of its useful life, steady indicates an hard fault. (factory service required?)

Reported by Gary Crutcher gcrutchr@nightflight.com

The boot message identifier for this drive is "".

This is a DDS-2 tape drive. DDS-2 means hardware data compression and narrower tracks for increased data capacity.

Native capacity is 24GB when using 120m tapes. This drive supports hardware data compression.

Data transfer rate is 510kB/s (native).

This drive is used in Hewlett-Packard's SureStore tape drive.

The drive has two selectors on the rear panel. The selector closer to the fan is SCSI id. The other selector should be set to 7.

There are four internal switches. These should be set: 1 ON; 2 ON; 3 ON; 4 OFF.

At present the kernel drivers do not automatically change tapes at the end of a volume. This shell script can be used to change tapes: #!/bin/sh PATH="/sbin:/usr/sbin:/bin:/usr/bin"; export PATH usage() { echo "Usage: dds_changer [123456ne] raw-device-name echo "1..6 = Select cartridge" echo "next cartridge" echo "eject magazine" exit 2 } if [ $# -ne 2 ] ; then usage fi cdb3=0 cdb4=0 cdb5=0 case $1 in [123456]) cdb3=$1 cdb4=1 ;; n) ;; e) cdb5=0x80 ;; ?) usage ;; esac scsi -f $2 -s 100 -c "1b 0 0 $cdb3 $cdb4 $cdb5"

The boot message identifier for this drive is "HP HP35450A -A C620" "type 1 removable SCSI 2" "Sequential-Access density code 0x13"

This is a DDS-1 tape drive. DDS-1 is the original DAT tape format.

Native capacity is 1.2GB.

Data transfer rate is 160kB/s.

Reported by: mark thompson mark.a.thompson@pobox.com

The boot message identifier for this drive is "HP HP35470A 9 09" type 1 removable SCSI 2"

This is a DDS-1 tape drive. DDS-1 is the original DAT tape format.

Native capacity is 2GB when using 90m tapes.

Data transfer rate is 183kB/s.

The same mechanism is used in Hewlett-Packard's SureStore tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT drive, and HP C1536A DDS format DAT drive.

Warning: Quality control on these drives varies greatly. One FreeBSD core-team member has returned 5 of these drives. None lasted more than 9 months.

Reported by: David Dawes dawes@rf900.physics.usyd.edu.au (9 09)

The boot message identifier for this drive is "HP HP35480A 1009" "type 1 removable SCSI 2" "Sequential-Access density code 0x13".

This is a DDS-DC tape drive. DDS-DC is DDS-1 with hardware data compression. DDS-1 is the original DAT tape format.

Native capacity is 2GB when using 90m tapes. It cannot handle 120m tapes. This drive supports hardware data compression. Please refer to the section on for the proper switch settings.

Data transfer rate is 183kB/s.

This drive is used in Hewlett-Packard's SureStore and tape drives and C35480A DDS format DAT drive..

This drive will occasionally hang during a tape eject operation (mt offline). Pressing the front panel button will eject the tape and bring the tape drive back to life.

WARNING: HP 35480-03110 only. On at least two occasions this tape drive when used with FreeBSD 2.1.0, an IBM Server 320 and an 2940W SCSI controller resulted in all SCSI disk partitions being lost. The problem has not be analyzed or resolved at this time.

There are at least two significantly different models: one is a DDS-1 and the other DDS-2. The DDS-1 version is "SDT-5000 3.02". The DDS-2 version is "SONY SDT-5000 327M". The DDS-2 version has a 1MB cache. This cache is able to keep the tape streaming in almost any circumstances.

The boot message identifier for this drive is "SONY SDT-5000 3.02" "type 1 removable SCSI 2" "Sequential-Access density code 0x13"

Native capacity is 4GB when using 120m tapes. This drive supports hardware data compression.

Data transfer rate is depends upon the model or the drive. The rate is 630kB/s for the "SONY SDT-5000 327M" while compressing the data. For the "SONY SDT-5000 3.02", the data transfer rate is 225kB/s.

In order to get this drive to stream, set the blocksize to 512 bytes (mt blocksize 512) reported by Kenneth Merry ken@ulc199.residence.gatech.edu"

"SONY SDT-5000 327M" information reported by Charles Henrich henrich@msu.edu

Reported by: &a.jmz;

The boot message identifier for this drive is "TANDBERG TDC 3600 =08:" "type 1 removable SCSI 2"

This is a QIC tape drive.

Native capacity is 150/250MB.

This drive has quirks which are known and work around code is present in the scsi tape device driver (st(4)). Upgrading the firmware to XXX version will fix the quirks and provide SCSI 2 capabilities.

Data transfer rate is 80kB/s.

IBM and Emerald units will not work. Replacing the firmware EPROM of these units will solve the problem.

Reported by: Michael Smith msmith@atrad.adelaide.edu.au

This is very similar to the drive.

Reported by: &a.joerg;

The boot message identifier for this drive is "TANDBERG TDC 4222 =07" "type 1 removable SCSI 2"

This is a QIC tape drive.

Native capacity is 2.5GB. The drive will read all cartridges from the 60 MB (DC600A) upwards, and write 150 MB (DC6150) upwards. Hardware compression is optionally supported for the 2.5 GB cartridges.

This drives quirks are known and pre-compiled into the scsi tape device driver (st(4)) beginning with FreeBSD 2.2-current. For previous versions of FreeBSD, use mt to read one block from the tape, rewind the tape, and then execute the backup program (mt fsr 1; mt rewind; dump ...)

Data transfer rate is 600kB/s (vendor claim with compression), 350 KB/s can even be reached in start/stop mode. The rate decreases for smaller cartridges.

Reported by: &a.joerg;

The boot message identifier for this drive is "WANGTEK 5525ES SCSI REV7 3R1" "type 1 removable SCSI 1" "density code 0x11, 1024-byte blocks"

This is a QIC tape drive.

Native capacity is 525MB.

Data transfer rate is 180kB/s.

The drive reads 60, 120, 150, and 525MB tapes. The drive will not write 60MB (DC600 cartridge) tapes. In order to overwrite 120 and 150 tapes reliably, first erase (mt erase) the tape. 120 and 150 tapes used a wider track (fewer tracks per tape) than 525MB tapes. The "extra" width of the previous tracks is not overwritten, as a result the new data lies in a band surrounded on both sides by the previous data unless the tape have been erased.

This drives quirks are known and pre-compiled into the scsi tape device driver (st(4)).

Other firmware revisions that are known to work are: M75D

Reported by: Marc van Kempen marc@bowtie.nl "REV73R1" Andrew Gordon Andrew.Gordon@net-tel.co.uk "M75D"

The boot message identifier for this drive is "WANGTEK 6200-HS 4B18" "type 1 removable SCSI 2" "Sequential-Access density code 0x13"

This is a DDS-1 tape drive.

Native capacity is 2GB using 90m tapes.

Data transfer rate is 150kB/s.

Reported by: Tony Kimball alk@Think.COM * Problem drives * CD-ROM drives +

Contributed by &a.obrien;.23 November 1997.

+

As mentioned in + + Generally speaking those in The FreeBSD Project prefer SCSI + CDROM drives over IDE CDROM drives. However not all SCSI CDROM drives + are equal. Some feel the quality of some SCSI CDROM drives have been + deteriorating to that of IDE CDROM drives. Toshiba used to be the + favored stand-by, but many on the SCSI mailing list have found + displeasure with the 12x speed XM-5701TA as its volume (when playing + audio CDROMs) is not controlable by the various audio player software. + + Another area where SCSI CDROM manufactors are cutting corners is + adhearance to the + . Many SCSI + CDROMs will repsond to + for its target address. + Known violators include the 6x Teac CD-56S 1.0D. + + + + * Other * Adding and reconfiguring disks Tapes and backups * What about backups to floppies? Tape Media

4mm tapes are replacing QIC as the workstation backup media of choice. This trend accelerated greatly when Conner purchased Archive, a leading manufacturer of QIC drives, and then stopped production of QIC drives. 4mm drives are small and quiet but do not have the reputation for reliability that is enjoyed by 8mm drives. The cartridges are less expensive and smaller (3 x 2 x 0.5 inches, 76 x 51 x 12 mm) than 8mm cartridges. 4mm, like 8mm, has comparatively short head life for the same reason, both use helical scan.

Data thruput on these drives starts ~150kB/s, peaking at ~500kB/s. Data capacity starts at 1.3 GB and ends at 2.0 GB. Hardware compression, available with most of these drives, approximately doubles the capacity. Multi-drive tape library units can have 6 drives in a single cabinet with automatic tape changing. Library capacities reach 240 GB.

4mm drives, like 8mm drives, use helical-scan. All the benefits and drawbacks of helical-scan apply to both 4mm and 8mm drives.

Tapes should be retired from use after 2,000 passes or 100 full backups.

8mm tapes are the most common SCSI tape drives; they are the best choice of exchanging tapes. Nearly every site has an exabyte 2 GB 8mm tape drive. 8mm drives are reliable, convenient and quiet. Cartridges are inexpensive and small (4.8 x 3.3 x 0.6 inches; 122 x 84 x 15 mm). One downside of 8mm tape is relatively short head and tape life due to the high rate of relative motion of the tape across the heads.

Data thruput ranges from ~250kB/s to ~500kB/s. Data sizes start at 300 MB and go up to 7 GB. Hardware compression, available with most of these drives, approximately doubles the capacity. These drives are available as single units or multi-drive tape libraries with 6 drives and 120 tapes in a single cabinet. Tapes are changed automatically by the unit. Library capacities reach 840+ GB.

Data is recorded onto the tape using helical-scan, the heads are positioned at an angle to the media (approximately 6 degrees). The tape wraps around 270 degrees of the spool that holds the heads. The spool spins while the tape slides over the spool. The result is a high density of data and closely packed tracks that angle across the tape from one edge to the other.

QIC-150 tapes and drives are, perhaps, the most common tape drive and media around. QIC tape drives are the least expensive "serious" backup drives. The downside is the cost of media. QIC tapes are expensive compared to 8mm or 4mm tapes, up to 5 times the price per GB data storage. But, if your needs can be satisfied with a half-dozen tapes, QIC may be the correct choice. QIC is the most common tape drive. Every site has a QIC drive of some density or another. Therein lies the rub, QIC has a large number of densities on physically similar (sometimes identical) tapes. QIC drives are not quiet. These drives audibly seek before they begin to record data and are clearly audible whenever reading, writing or seeking. QIC tapes measure (6 x 4 x 0.7 inches; 15.2 x 10.2 x 1.7 mm). , which also use 1/4" wide tape are discussed separately. Tape libraries and changers are not available.

Data thruput ranges from ~150kB/s to ~500kB/s. Data capacity ranges from 40 MB to 15 GB. Hardware compression is available on many of the newer QIC drives. QIC drives are less frequently installed; they are being supplanted by DAT drives.

Data is recorded onto the tape in tracks. The tracks run along the long axis of the tape media from one end to the other. The number of tracks, and therefore the width of a track, varies with the tape's capacity. Most if not all newer drives provide backward-compatibility at least for reading (but often also for writing). QIC has a good reputation regarding the safety of the data (the mechanics are simpler and more robust than for helical scan drives).

Tapes should be retired from use after 5,000 backups.

DLT has the fastest data transfer rate of all the drive types listed here. The 1/2" (12.5mm) tape is contained in a single spool cartridge (4 x 4 x 1 inches; 100 x 100 x 25 mm). The cartridge has a swinging gate along one entire side of the cartridge. The drive mechanism opens this gate to extract the tape leader. The tape leader has an oval hole in it which the drive uses to "hook" the tape. The take-up spool is located inside the tape drive. All the other tape cartridges listed here (9 track tapes are the only exception) have both the supply and take-up spools located inside the tape cartridge itself. Data thruput is approximately 1.5MB/s, three times the thruput of 4mm, 8mm, or QIC tape drives. Data capacities range from 10GB to 20GB for a single drive. Drives are available in both multi-tape changers and multi-tape, multi-drive tape libraries containing from 5 to 900 tapes over 1 to 20 drives, providing from 50GB to 9TB of storage. Data is recorded onto the tape in tracks parallel to the direction of travel (just like QIC tapes). Two tracks are written at once. Read/write head lifetimes are relatively long; once the tape stops moving, there is no relative motion between the heads and the tape. Using a new tape for the first time

The first time that you try to read or write a new, completely blank tape, the operation will fail. The console messages should be similar to: st0(ncr1:4:0): NOT READY asc:4,1 st0(ncr1:4:0): Logical unit is in process of becoming ready The tape does not contain an Identifier Block (block number 0). All QIC tape drives since the adoption of QIC-525 standard write an Identifier Block to the tape. There are two solutions:

mt fsf 1 causes the tape drive to write an Identifier Block to the tape.

Use the front panel button to eject the tape.

Re-insert the tape and dump(8) data to the tape.

dump(8) will report DUMP: End of tape detected and the console will show: HARDWARE FAILURE info:280 asc:80,96

rewind the tape using: mt rewind

Subsequent tape operations are successful. Backup Programs

The three major programs are dump(8), tar(1), and cpio(1). Dump and Restore

dump(8) and restore(8) are the traditional Unix backup programs. They operate on the drive as a collection of disk blocks, below the abstractions of files, links and directories that are created by the filesystems. dump(8) backs up devices, entire filesystems, not parts of a filesystem and not directory trees that span more than one filesystem, using either soft links ln(1) or mounting one filesystem onto another. dump(8) does not write files and directories to tape, but rather writes the data blocks that are the building blocks of files and directories. dump(8) has quirks that remain from its early days in Version 6 of ATT Unix (circa 1975). The default parameters are suitable for 9-track tapes (6250 bpi), not the high-density media available today (up to 62,182 ftpi). These defaults must be overridden on the command line to utilize the capacity of current tape drives.

rdump(8) and rrestore(8) backup data across the network to a tape drive attached to another computer. Both programs rely upon rcmd(3) and ruserok(3) to access the remote tape drive. Therefore, the user performing the backup must have rhosts access to the remote computer. The arguments to rdump(8) and rrestore(8) must suitable to use on the remote computer. (e.g. When rdump'ing from a FreeBSD computer to an Exabyte tape drive connected to a Sun called komodo, use: /sbin/rdump 0dsbfu 54000 13000 126 komodo:/dev/nrst8 /dev/rsd0a 2>&1) Beware: there are security implications to allowing rhosts commands. Evaluate your situation carefully. Tar

tar(1) also dates back to Version 6 of ATT Unix (circa 1975). tar(1) operates in cooperation with the filesystem; tar(1) writes files and directories to tape. tar(1) does not support the full range of options that are available from cpio(1), but tar(1) does not require the unusual command pipeline that cpio(1) uses.

Most versions of tar(1) do not support backups across the network. The GNU version of tar(1), which FreeBSD utilizes, supports remote devices using the same syntax as rdump. To tar(1) to an Exabyte tape drive connected to a Sun called komodo, use: /usr/bin/tar cf komodo:/dev/nrst8 . 2>&1. For versions without remote device support, you can use a pipeline and rsh(1) to send the data to a remote tape drive. (XXX add an example command) Cpio

cpio(1) is the original Unix file interchange tape program for magnetic media. cpio(1) has options (among many others) to perform byte-swapping, write a number of different archives format, and pipe the data to other programs. This last feature makes cpio(1) and excellent choice for installation media. cpio(1) does not know how to walk the directory tree and a list of files must be provided thru STDIN.

cpio(1) does not support backups across the network. You can use a pipeline and rsh(1) to send the data to a remote tape drive. (XXX add an example command) Pax

pax(1) is IEEE/POSIX's answer to tar and cpio. Over the years the various versions of tar and cpio have gotten slightly incompatable. So rather than fight it out to fully standardize them, POSIX created a new archive utilility. pax attempts to read and write many of the various cpio and tar formats, plus new formats of its own. Its command set more resembles cpio than tar.

Amanda (Advanced Maryland Network Disk Archiver) is a client/server backup system, rather than a single program. An Amanda server will backup to a single tape drive any number of computers that have Amanda clients and network communications with the Amanda server. A common problem at locations with a number of large disks is the length of time required to backup to data directly to tape exceeds the amount of time available for the task. Amanda solves this problem. Amanda can use a "holding disk" to backup several filesystems at the same time. Amanda creates "archive sets": a group of tapes used over a period of time to create full backups of all the filesystems listed in Amanda's configuration file. The "archive set" also contains nightly incremental (or differential) backups of all the filesystems. Restoring a damaged filesystem requires the most recent full backup and the incremental backups.

The configuration file provides fine control backups and the network traffic that Amanda generates. Amanda will use any of the above backup programs to write the data to tape. Amanda is available as either a port or a package, it is not installed by default. Do nothing

"Do nothing" is not a computer program, but it is the most widely used backup strategy. There are no initial costs. There is no backup schedule to follow. Just say no. If something happens to your data, grin and bear it!

If your time and your data is worth little to nothing, then "Do nothing" is the most suitable backup program for your computer. But beware, Unix is a useful tool, you may find that within six months you have a collection of files that are valuable to you.

"Do nothing" is the correct backup method for /usr/obj and other directory trees that can be exactly recreated by your computer. An example is the files that comprise these handbook pages-they have been generated from SGML input files. Creating backups of these HTML files is not necessary. The SGML source files are backed up regularly. Which Backup Program is Best?

dump(8) Period. Elizabeth D. Zwicky torture tested all the backup programs discussed here. The clear choice for preserving all your data and all the peculiarities of Unix filesystems is dump(8). Elizabeth created filesystems containing a large variety of unusual conditions (and some not so unusual ones) and tested each program by do a backup and restore of that filesystems. The peculiarities included: files with holes, files with holes and a block of nulls, files with funny characters in their names, unreadable and unwriteable files, devices, files that change size during the backup, files that are created/deleted during the backup and more. She presented the results at LISA V in Oct. 1991. Emergency Restore Procedure Before the Disaster

There are only four steps that you need to perform in preparation for any disaster that may occur.

First, print the disklabel from each of your disks (e.g. disklabel sd0 | lpr), your filesystem table (/etc/fstab) and all boot messages, two copies of each.

Second, determine the boot and fixit floppies (boot.flp and fixit.flp) have all your devices. The easiest way to check is to reboot your machine with the boot floppy in the floppy drive and check the boot messages. If all your devices are listed and functional, skip on to step three.

Otherwise, you have to create two custom bootable floppies which has a kernel that can mount your all of your disks and access your tape drive. These floppies must contain: fdisk(8), disklabel(8), newfs(8), mount(8), and whichever backup program you use. These programs must be statically linked. If you use dump(8), the floppy must contain restore(8).

Third, create backup tapes regularly. Any changes that you make after your last backup may be irretrievably lost. Write-protect the backup tapes.

Fourth, test the floppies (either boot.flp and fixit.flp or the two custom bootable floppies you made in step two.) and backup tapes. Make notes of the procedure. Store these notes with the bootable floppy, the printouts and the backup tapes. You will be so distraught when restoring that the notes may prevent you from destroying your backup tapes (How? In place of tar xvf /dev/rst0, you might accidently type tar cvf /dev/rst0 and over-write your backup tape).

For an added measure of security, make bootable floppies and two backup tapes each time. Store one of each at a remote location. A remote location is NOT the basement of the same office building. A number of firms in the World Trade Center learned this lesson the hard way. A remote location should be physically separated from your computers and disk drives by a significant distance.

An example script for creating a bootable floppy: #!/bin/sh # # create a restore floppy # # format the floppy # PATH=/bin:/sbin:/usr/sbin:/usr/bin fdformat -q fd0 if [ $? -ne 0 ] then echo "Bad floppy, please use a new one" exit 1 fi # place boot blocks on the floppy # disklabel -w -B -b /usr/mdec/fdboot -s /usr/mdec/bootfd /dev/rfd0c fd1440 # # newfs the one and only partition # newfs -t 2 -u 18 -l 1 -c 40 -i 5120 -m 5 -o space /dev/rfd0a # # mount the new floppy # mount /dev/fd0a /mnt # # create required directories # mkdir /mnt/dev mkdir /mnt/bin mkdir /mnt/sbin mkdir /mnt/etc mkdir /mnt/root mkdir /mnt/mnt # for the root partition mkdir /mnt/tmp mkdir /mnt/var # # populate the directories # if [ ! -x /sys/compile/MINI/kernel ] then cat << EOM The MINI kernel does not exist, please create one. Here is an example config file: # # MINI -- A kernel to get FreeBSD on onto a disk. # machine "i386" cpu "I486_CPU" ident MINI maxusers 5 options INET # needed for _tcp _icmpstat _ipstat # _udpstat _tcpstat _udb options FFS #Berkeley Fast File System options FAT_CURSOR #block cursor in syscons or pccons options SCSI_DELAY=15 #Be pessimistic about Joe SCSI device options NCONS=2 #1 virtual consoles options USERCONFIG #Allow user configuration with -c XXX config kernel root on sd0 swap on sd0 and sd1 dumps on sd0 controller isa0 controller pci0 controller fdc0 at isa? port "IO_FD1" bio irq 6 drq 2 vector fdintr disk fd0 at fdc0 drive 0 controller ncr0 controller scbus0 device sc0 at isa? port "IO_KBD" tty irq 1 vector scintr device npx0 at isa? port "IO_NPX" irq 13 vector npxintr device sd0 device sd1 device sd2 device st0 pseudo-device loop # required by INET pseudo-device gzip # Exec gzipped a.out's EOM exit 1 fi cp -f /sys/compile/MINI/kernel /mnt gzip -c -best /sbin/init > /mnt/sbin/init gzip -c -best /sbin/fsck > /mnt/sbin/fsck gzip -c -best /sbin/mount > /mnt/sbin/mount gzip -c -best /sbin/halt > /mnt/sbin/halt gzip -c -best /sbin/restore > /mnt/sbin/restore gzip -c -best /bin/sh > /mnt/bin/sh gzip -c -best /bin/sync > /mnt/bin/sync cp /root/.profile /mnt/root cp -f /dev/MAKEDEV /mnt/dev chmod 755 /mnt/dev/MAKEDEV chmod 500 /mnt/sbin/init chmod 555 /mnt/sbin/fsck /mnt/sbin/mount /mnt/sbin/halt chmod 555 /mnt/bin/sh /mnt/bin/sync chmod 6555 /mnt/sbin/restore # # create the devices nodes # cd /mnt/dev ./MAKEDEV std ./MAKEDEV sd0 ./MAKEDEV sd1 ./MAKEDEV sd2 ./MAKEDEV st0 ./MAKEDEV pty0 cd / # # create minimum filesystem table # cat > /mnt/etc/fstab < /mnt/etc/passwd < /mnt/etc/master.passwd < After the Disaster

The key question is: did your hardware survive? You have been doing regular backups so there is no need to worry about the software.

If the hardware has been damaged. First, replace those parts that have been damaged.

If your hardware is okay, check your floppies. If you are using a custom boot floppy, boot single-user (type "-s" at the "boot:" prompt). Skip the following paragraph.

If you are using the boot.flp and fixit.flp floppies, keep reading. Insert the boot.flp floppy in the first floppy drive and boot the computer. The original install menu will be displayed on the screen. Select the "Fixit--Repair mode with CDROM or floppy." option. Insert the fixit.flp when prompted. restore and the other programs that you need are located in /mnt2/stand.

Recover each filesystem separately.

Try to mount(8) (e.g. mount /dev/sd0a /mnt) the root partition of your first disk. If the disklabel was damaged, use disklabel(8) to re-partition and label the disk to match the label that your printed and saved. Use newfs(8) to re-create the filesystems. Re-mount the root partition of the floppy read-write ("mount -u -o rw /mnt"). Use your backup program and backup tapes to recover the data for this filesystem (e.g. restore vrf /dev/st0). Unmount the filesystem (e.g. umount /mnt) Repeat for each filesystem that was damaged.

Once your system is running, backup your data onto new tapes. Whatever caused the crash or data loss may strike again. An another hour spent now, may save you from further distress later. * I did not prepare for the Disaster, What Now? * Serial ports * Sound cards * PCMCIA * Other diff --git a/handbook/scsi.sgml b/handbook/scsi.sgml index d02b89a87a..59706eeb31 100644 --- a/handbook/scsi.sgml +++ b/handbook/scsi.sgml @@ -1,891 +1,892 @@ - + What is SCSI?

Copyright © 1995, &a.wilko;.July 6, 1996. SCSI is an acronym for Small Computer Systems Interface. It is an ANSI standard that has become one of the leading I/O buses in the computer industry. The foundation of the SCSI standard was laid by Shugart Associates (the same guys that gave the world the first mini floppy disks) when they introduced the SASI bus (Shugart Associates Standard Interface). After some time an industry effort was started to come to a more strict standard allowing devices from different vendors to work together. This effort was recognized in the ANSI SCSI-1 standard. The SCSI-1 standard (approx 1985) is rapidly becoming obsolete. The current standard is SCSI-2 (see ), with SCSI-3 on the drawing boards. In addition to a physical interconnection standard, SCSI defines a logical (command set) standard to which disk devices must adhere. This standard is called the Common Command Set (CCS) and was developed more or less in parallel with ANSI SCSI-1. SCSI-2 includes the (revised) CCS as part of the standard itself. The commands are dependent on the type of device at hand. It does not make much sense of course to define a Write command for a scanner. The SCSI bus is a parallel bus, which comes in a number of variants. The oldest and most used is an 8 bit wide bus, with single-ended signals, carried on 50 wires. (If you do not know what single-ended means, do not worry, that is what this document is all about.) Modern designs also use 16 bit wide buses, with differential signals. This allows transfer speeds of 20Mbytes/second, on cables lengths of up to 25 meters. SCSI-2 allows a maximum bus width of 32 bits, using an additional cable. Quickly emerging are Ultra SCSI (also called Fast-20) and Ultra2 (also called Fast-40). Fast-20 is 20 mega-transfers per second (20 Mbytes/sec on a 8 bit bus), Fast-40 is 40 mega-transfers per second (40 Mbytes/sec on a 8 bit bus). Of course the SCSI bus not only has data lines, but also a number of control signals. A very elaborate protocol is part of the standard to allow multiple devices to share the bus in an efficient manner. In SCSI-2, the data is always checked using a separate parity line. In pre-SCSI-2 designs parity was optional. In SCSI-3 even faster bus types are introduced, along with a serial SCSI busses that reduces the cabling overhead and allows a higher maximum bus length. You might see names like SSA and Fiberchannel in this context. None of the serial buses are currently in widespread use (especially not in the typical FreeBSD environment). For this reason the serial bus types are not discussed any further. As you could have guessed from the description above, SCSI devices are intelligent. They have to be to adhere to the SCSI standard (which is over 2 inches thick BTW). So, for a hard disk drive for instance you do not specify a head/cylinder/sector to address a particular block, but simply the number of the block you want. Elaborate caching schemes, automatic bad block replacement etc are all made possible by this 'intelligent device' approach. On a SCSI bus, each possible pair of devices can communicate. Whether their function allows this is another matter, but the standard does not restrict it. To avoid signal contention, the 2 devices have to arbitrate for the bus before using it. The philosophy of SCSI is to have a standard that allows older-standard devices to work with newer-standard ones. So, an old SCSI-1 device should normally work on a SCSI-2 bus. I say Normally, because it is not absolutely sure that the implementation of an old device follows the (old) standard closely enough to be acceptable on a new bus. Modern devices are usually more well-behaved, because the standardization has become more strict and is better adhered to by the device manufacturers. Generally speaking, the chances of getting a working set of devices on a single bus is better when all the devices are SCSI-2 or newer. This implies that you do not have to dump all your old stuff when you get that shiny 2Gb disk: I own a system on which a pre-SCSI-1 disk, a SCSI-2 QIC tape unit, a SCSI-1 helical scan tape unit and 2 SCSI-1 disks work together quite happily. From a performance standpoint you might want to separate your older and newer (=faster) devices however. Components of SCSI

As said before, SCSI devices are smart. The idea is to put the knowledge about intimate hardware details onto the SCSI device itself. In this way, the host system does not have to worry about things like how many heads are hard disks has, or how many tracks there are on a specific tape device. If you are curious, the standard specifies commands with which you can query your devices on their hardware particulars. FreeBSD uses this capability during boot to check out what devices are connected and whether they need any special treatment. The advantage of intelligent devices is obvious: the device drivers on the host can be made in a much more generic fashion, there is no longer a need to change (and qualify!) drivers for every odd new device that is introduced. For cabling and connectors there is a golden rule: get good stuff. With bus speeds going up all the time you will save yourself a lot of grief by using good material. So, gold plated connectors, shielded cabling, sturdy connector hoods with strain reliefs etc are the way to go. Second golden rule: do no use cables longer than necessary. I once spent 3 days hunting down a problem with a flaky machine only to discover that shortening the SCSI bus by 1 meter solved the problem. And the original bus length was well within the SCSI specification. SCSI bus types

From an electrical point of view, there are two incompatible bus types: single-ended and differential. This means that there are two different main groups of SCSI devices and controllers, which cannot be mixed on the same bus. It is possible however to use special converter hardware to transform a single-ended bus into a differential one (and vice versa). The differences between the bus types are explained in the next sections. In lots of SCSI related documentation there is a sort of jargon in use to abbreviate the different bus types. A small list: FWD: Fast Wide Differential FND: Fast Narrow Differential SE: Single Ended FN: Fast Narrow etc. With a minor amount of imagination one can usually imagine what is meant. Wide is a bit ambiguous, it can indicate 16 or 32 bit buses. As far as I know, the 32 bit variant is not (yet) in use, so wide normally means 16 bit. Fast means that the timing on the bus is somewhat different, so that on a narrow (8 bit) bus 10 Mbytes/sec are possible instead of 5 Mbytes/sec for 'slow' SCSI. As discussed before, bus speeds of 20 and 40 megatransfers/second are also emerging (Fast-20 == Ultra SCSI and Fast-40 == Ultra2 SCSI). It should be noted that the data lines > 8 are only used for data transfers and device addressing. The transfers of commands and status messages etc are only performed on the lowest 8 data lines. The standard allows narrow devices to operate on a wide bus. The usable bus width is negotiated between the devices. You have to watch your device addressing closely when mixing wide and narrow. Single ended buses

A single-ended SCSI bus uses signals that are either 5 Volts or 0 Volts (indeed, TTL levels) and are relative to a COMMON ground reference. A singled ended 8 bit SCSI bus has approximately 25 ground lines, who are all tied to a single `rail' on all devices. A standard single ended bus has a maximum length of 6 meters. If the same bus is used with fast-SCSI devices, the maximum length allowed drops to 3 meters. Fast-SCSI means that instead of 5Mbytes/sec the bus allows 10Mbytes/sec transfers. Fast-20 (Ultra SCSI) and Fast-40 allow for 20 and 40 megatransfers/second respectively. So, F20 is 20 Mbytes/second on a 8 bit bus, 40 Mbytes/second on a 16 bit bus etc. For F20 the max bus length is 1.5 meters, for F40 it becomes 0.75 meters. Be aware that F20 is pushing the limits quite a bit, so you will quickly find out if your SCSI bus is electrically sound. Please note that this means that if some devices on your bus use 'fast' to communicate your bus must adhere to the length restrictions for fast buses! It is obvious that with the newer fast-SCSI devices the bus length can become a real bottleneck. This is why the differential SCSI bus was introduced in the SCSI-2 standard. For connector pinning and connector types please refer to the SCSI-2 standard (see ) itself, connectors etc are listed there in painstaking detail. Beware of devices using non-standard cabling. For instance Apple uses a 25pin D-type connecter (like the one on serial ports and parallel printers). Considering that the official SCSI bus needs 50 pins you can imagine the use of this connector needs some 'creative cabling'. The reduction of the number of ground wires they used is a bad idea, you better stick to 50 pins cabling in accordance with the SCSI standard. For Fast-20 and 40 do not even think about buses like this. Differential buses

A differential SCSI bus has a maximum length of 25 meters. Quite a difference from the 3 meters for a single-ended fast-SCSI bus. The idea behind differential signals is that each bus signal has its own return wire. So, each signal is carried on a (preferably twisted) pair of wires. The voltage difference between these two wires determines whether the signal is asserted or de-asserted. To a certain extent the voltage difference between ground and the signal wire pair is not relevant (do not try 10 kVolts though). It is beyond the scope of this document to explain why this differential idea is so much better. Just accept that electrically seen the use of differential signals gives a much better noise margin. You will normally find differential buses in use for inter-cabinet connections. Because of the lower cost single ended is mostly used for shorter buses like inside cabinets. There is nothing that stops you from using differential stuff with FreeBSD, as long as you use a controller that has device driver support in FreeBSD. As an example, Adaptec marketed the AHA1740 as a single ended board, whereas the AHA1744 was differential. The software interface to the host is identical for both. Terminators

Terminators in SCSI terminology are resistor networks that are used to get a correct impedance matching. Impedance matching is important to get clean signals on the bus, without reflections or ringing. If you once made a long distance telephone call on a bad line you probably know what reflections are. With 20Mbytes/sec traveling over your SCSI bus, you do not want signals echoing back. Terminators come in various incarnations, with more or less sophisticated designs. Of course, there are internal and external variants. Almost every SCSI device comes with a number of sockets in which a number of resistor networks can (must be!) installed. If you remove terminators from a device, carefully store them. You will need them when you ever decide to reconfigure your SCSI bus. There is enough variation in even these simple tiny things to make finding the exact replacement a frustrating business. There are also SCSI devices that have a single jumper to enable or disable a built-in terminator. There are special terminators you can stick onto a flat cable bus. Others look like external connectors, or a connector hood without a cable. So, lots of choice as you can see. There is much debate going on if and when you should switch from simple resistor (passive) terminators to active terminators. Active terminators contain slightly more elaborate circuit to give cleaner bus signals. The general consensus seems to be that the usefulness of active termination increases when you have long buses and/or fast devices. If you ever have problems with your SCSI buses you might consider trying an active terminator. Try to borrow one first, they reputedly are quite expensive. Please keep in mind that terminators for differential and single-ended buses are not identical. You should not mix the two variants. OK, and now where should you install your terminators? This is by far the most misunderstood part of SCSI. And it is by far the simplest. The rule is: every SCSI bus has 2 (two) terminators, one at each end of the bus. So, two and not one or three or whatever. Do yourself a favor and stick to this rule. It will save you endless grief, because wrong termination has the potential to introduce highly mysterious bugs. A common pitfall is to have an internal (flat)cable in a machine and also an external cable attached to the controller. It seems almost everybody forgets to remove the terminators from the controller. The terminator must now be on the last external device, and not on the controller! In general, every reconfiguration of a SCSI bus must pay attention to this. What I did myself is remove all terminators from my SCSI devices and controllers. I own a couple of external terminators, for both the Centronics-type external cabling and for the internal flat cable connectors. This makes reconfiguration much easier. On modern devices, sometimes integrated terminators are used. These things are special purpose integrated circuits that can be dis/en-abled with a control pin. It is not necessary to physically remove them from a device. You may find them on newer host adapters, sometimes they even are software configurable, using some sort of setup tool. Consult you documentation! Terminator power

The terminators discussed in the previous chapter need power to operate properly. On the SCSI bus, a line is dedicated to this purpose. So, simple huh? Not so. Each device can provide its own terminator power to the terminator sockets it has on-device. But if you have external terminators, or when the device supplying the terminator power to the SCSI bus line is switched off you are in trouble. The idea is that initiators (these are devices that initiate actions on the bus, a discussion follows) must supply terminator power. All SCSI devices are allowed (but not required) to supply terminator power. To allow for un-powered devices on a bus, the terminator power must be supplied to the bus via a diode. This prevents the backflow of current to un-powered devices. To prevent all kinds of nastiness, the terminator power is usually fused. As you can imagine, fuses might blow. This can, but does not have to, lead to a non functional bus. If multiple devices supply terminator power, a single blown fuse will not put you out of business. A single supplier with a blown fuse certainly will. Clever external terminators sometimes have a LED indication that shows whether terminator power is present. In newer designs auto-restoring fuses that 'reset' themselves after some time are sometimes used. Device addressing

Because the SCSI bus is, ehh, a bus there must be a way to distinguish or address the different devices connected to it. This is done by means of the SCSI or target ID. Each device has a unique target ID. You can select the ID to which a device must respond using a set of jumpers, or a dip switch, or something similar. Consult the documentation of your device for more information. Beware of multiple devices configured to use the same ID. Chaos normally reigns in this case. A pitfall is that one of the devices sharing the same ID sometimes even manages to answer to I/O requests! For an 8 bit bus, a maximum of 8 targets is possible. The maximum is 8 because the selection is done bitwise using the 8 data lines on the bus. For wide buses this increases to the number of data lines. The higher the SCSI target ID, the higher the priority the devices has. When it comes to arbitration between devices that want to use the bus at the same time, the device that has the highest SCSI ID will win. This also means that the SCSI host adapter usually uses target ID 7 (for narrow buses). For a further subdivision, the standard allows for Logical Units or LUNs for short. A single target ID may have multiple LUNs. For example, a tape device including a tape changer may have LUN 0 for the tape device itself, and LUN 1 for the tape changer. In this way, the host system can address each of the functional units of the tape changer as desired. Bus layout

SCSI buses are linear. So, not shaped like Y-junctions, star topologies, cobwebs or whatever else people might want to invent. You might notice that the terminator issue discussed earlier becomes rather hairy if your bus is not linear. The electrical characteristics, its noise margins and ultimately the reliability of it all are tightly related to linear bus rule. Stick to the linear bus rule! Using SCSI with FreeBSD

About translations, BIOSes and magic...

As stated before, you should first make sure that you have a electrically sound bus. When you want to use a SCSI disk on your PC as boot disk, you must aware of some quirks related to PC BIOSes. The PC BIOS in its first incarnation used a low level physical interface to the hard disk. So, you had to tell the BIOS (using a setup tool or a BIOS built-in setup) how your disk physically looked like. This involved stating number of heads, number of cylinders, number of sectors per track, obscure things like precompensation and reduced write current cylinder etc. One might be inclined to think that since SCSI disks are smart you can forget about this. Alas, the arcane setup issue is still present today. The system BIOS needs to know how to access your SCSI disk with the head/cyl/sector method in order to load the FreeBSD kernel during boot. The SCSI host adapter or SCSI controller you have put in your AT/EISA/PCI/whatever bus to connect your disk therefore has its own on-board BIOS. During system startup, the SCSI BIOS takes over the hard disk interface routines from the system BIOS. To fool the system BIOS, the system setup is normally set to No hard disk present. Obvious, isn't it? The SCSI BIOS itself presents to the system a so called translated drive. This means that a fake drive table is constructed that allows the PC to boot the drive. This translation is often (but not always) done using a pseudo drive with 64 heads and 32 sectors per track. By varying the number of cylinders, the SCSI BIOS adapts to the actual drive size. It is useful to note that 32 * 64 / 2 = the size of your drive in megabytes. The division by 2 is to get from disk blocks that are normally 512 bytes in size to Kbytes. Right. All is well now?! No, it is not. The system BIOS has another quirk you might run into. The number of cylinders of a bootable hard disk cannot be greater than 1024. Using the translation above, this is a show-stopper for disks greater than 1 Gb. With disk capacities going up all the time this is causing problems. Fortunately, the solution is simple: just use another translation, e.g. with 128 heads instead of 32. In most cases new SCSI BIOS versions are available to upgrade older SCSI host adapters. Some newer adapters have an option, in the form of a jumper or software setup selection, to switch the translation the SCSI BIOS uses. It is very important that all operating systems on the disk use the same translation to get the right idea about where to find the relevant partitions. So, when installing FreeBSD you must answer any questions about heads/cylinders etc using the translated values your host adapter uses. Failing to observe the translation issue might lead to un-bootable systems or operating systems overwriting each others partitions. Using fdisk you should be able to see all partitions. You might have heard some talk of 'lying' devices? Older FreeBSD kernels used to report the geometry of SCSI disks when booting. An example from one of my systems: aha0 targ 0 lun 0: sd0: 636MB (1303250 total sec), 1632 cyl, 15 head, 53 sec, bytes/sec 512 Newer kernels usually do not report this information. e.g. (bt0:0:0): "SEAGATE ST41651 7574" type 0 fixed SCSI 2 sd0(bt0:0:0): Direct-Access 1350MB (2766300 512 byte sectors) Why has this changed? This info is retrieved from the SCSI disk itself. Newer disks often use a technique called zone bit recording. The idea is that on the outer cylinders of the drive there is more space so more sectors per track can be put on them. This results in disks that have more tracks on outer cylinders than on the inner cylinders and, last but not least, have more capacity. You can imagine that the value reported by the drive when inquiring about the geometry now becomes suspect at best, and nearly always misleading. When asked for a geometry , it is nearly always better to supply the geometry used by the BIOS, or if the BIOS is never going to know about this disk, (e.g. it is not a booting disk) to supply a fictitious geometry that is convenient. SCSI subsystem design

FreeBSD uses a layered SCSI subsystem. For each different controller card a device driver is written. This driver knows all the intimate details about the hardware it controls. The driver has a interface to the upper layers of the SCSI subsystem through which it receives its commands and reports back any status. On top of the card drivers there are a number of more generic drivers for a class of devices. More specific: a driver for tape devices (abbreviation: st), magnetic disks (sd), cdroms (cd) etc. In case you are wondering where you can find this stuff, it all lives in /sys/scsi. See the man pages in section 4 for more details. The multi level design allows a decoupling of low-level bit banging and more high level stuff. Adding support for another piece of hardware is a much more manageable problem. Kernel configuration

Dependent on your hardware, the kernel configuration file must contain one or more lines describing your host adapter(s). This includes I/O addresses, interrupts etc. Consult the man page for your adapter driver to get more info. Apart from that, check out /sys/i386/conf/LINT for an overview of a kernel config file. LINT contains every possible option you can dream of. It does not imply LINT will actually get you to a working kernel at all. Although it is probably stating the obvious: the kernel config file should reflect your actual hardware setup. So, interrupts, I/O addresses etc must match the kernel config file. During system boot messages will be displayed to indicate whether the configured hardware was actually found. An example loosely based on the FreeBSD 2.0.5-Release kernel config file LINT with some added comments (between []): # SCSI host adapters: `aha', `ahb', `aic', `bt', `nca' # # aha: Adaptec 154x # ahb: Adaptec 174x # ahc: Adaptec 274x/284x/294x # aic: Adaptec 152x and sound cards using the Adaptec AIC-6360 (slow!) # bt: Most Buslogic controllers # nca: ProAudioSpectrum cards using the NCR 5380 or Trantor T130 # uha: UltraStore 14F and 34F # sea: Seagate ST01/02 8 bit controller (slow!) # wds: Western Digital WD7000 controller (no scatter/gather!). # [For an Adaptec AHA274x, 284x etc controller] controller ahc0 at isa? bio irq ? vector ahcintr # port??? iomem? [For an Adaptec AHA174x controller] controller ahb0 at isa? bio irq ? vector ahbintr [For an Ultrastor adapter] controller uha0 at isa? port "IO_UHA0" bio irq ? drq 5 vector uhaintr # Map SCSI buses to specific SCSI adapters controller scbus0 at ahc0 controller scbus2 at ahb0 controller scbus1 at uha0 # The actual SCSI devices disk sd0 at scbus0 target 0 unit 0 [SCSI disk 0 is at scbus 0, LUN 0] disk sd1 at scbus0 target 1 [implicit LUN 0 if omitted] disk sd2 at scbus1 target 3 [SCSI disk on the uha0] disk sd3 at scbus2 target 4 [SCSI disk on the ahb0] tape st1 at scbus0 target 6 [SCSI tape at target 6] device cd0 at scbus? [the first ever CDROM found, no wiring] The example above tells the kernel to look for a ahc (Adaptec 274x) controller, then for an Adaptec 174x board, and so on. The lines following the controller specifications tell the kernel to configure specific devices but only attach them when they match the target ID and LUN specified on the corresponding bus. Wired down devices get 'first shot' at the unit numbers so the first non 'wired down' device, is allocated the unit number one greater than the highest 'wired down' unit number for that kind of device. So, if you had a SCSI tape at target ID 2 it would be configured as st2, as the tape at target ID 6 is wired down to unit number 1. Note that wired down devices need not be found to get their unit number. The unit number for a wired down device is reserved for that device, even if it is turned off at boot time. This allows the device to be turned on and brought on-line at a later time, without rebooting. Notice that a device's unit number has no relationship with its target ID on the SCSI bus. Below is another example of a kernel config file as used by FreeBSD version < 2.0.5. The difference with the first example is that devices are not 'wired down'. 'Wired down' means that you specify which SCSI target belongs to which device. A kernel built to the config file below will attach the first SCSI disk it finds to sd0, the second disk to sd1 etc. If you ever removed or added a disk, all other devices of the same type (disk in this case) would 'move around'. This implies you have to change /etc/fstab each time. Although the old style still works, you are strongly recommended to use this new feature. It will save you a lot of grief whenever you shift your hardware around on the SCSI buses. So, when you re-use your old trusty config file after upgrading from a pre-FreeBSD2.0.5.R system check this out. [driver for Adaptec 174x] controller ahb0 at isa? bio irq 11 vector ahbintr [for Adaptec 154x] controller aha0 at isa? port "IO_AHA0" bio irq 11 drq 5 vector ahaintr [for Seagate ST01/02] controller sea0 at isa? bio irq 5 iomem 0xc8000 iosiz 0x2000 vector seaintr controller scbus0 device sd0 [support for 4 SCSI harddisks, sd0 up sd3] device st0 [support for 2 SCSI tapes] [for the cdrom] device cd0 #Only need one of these, the code dynamically grows Both examples support SCSI disks. If during boot more devices of a specific type (e.g. sd disks) are found than are configured in the booting kernel, the system will simply allocate more devices, incrementing the unit number starting at the last number 'wired down'. If there are no 'wired down' devices then counting starts at unit 0. Use man 4 scsi to check for the latest info on the SCSI subsystem. For more detailed info on host adapter drivers use eg man 4 aha for info on the Adaptec 154x driver. Tuning your SCSI kernel setup

Experience has shown that some devices are slow to respond to INQUIRY commands after a SCSI bus reset (which happens at boot time). An INQUIRY command is sent by the kernel on boot to see what kind of device (disk, tape, CDROM etc) is connected to a specific target ID. This process is called device probing by the way. To work around the 'slow response' problem, FreeBSD allows a tunable delay time before the SCSI devices are probed following a SCSI bus reset. You can set this delay time in your kernel configuration file using a line like: options SCSI_DELAY=15 #Be pessimistic about Joe SCSI device This line sets the delay time to 15 seconds. On my own system I had to use 3 seconds minimum to get my trusty old CDROM drive to be recognized. Start with a high value (say 30 seconds or so) when you have problems with device recognition. If this helps, tune it back until it just stays working. - Rogue SCSI devices + Rogue SCSI devices

Although the SCSI standard tries to be complete and concise, it is a complex standard and implementing things correctly is no easy task. Some vendors do a better job then others. This is exactly where the 'rogue' devices come into view. Rogues are devices that are recognized by the FreeBSD kernel as behaving slightly (...) non-standard. Rogue devices are reported by the kernel when booting. An example for two of my cartridge tape units: Feb 25 21:03:34 yedi /kernel: ahb0 targ 5 lun 0: Feb 25 21:03:34 yedi /kernel: st0: Tandberg tdc3600 is a known rogue Mar 29 21:16:37 yedi /kernel: aha0 targ 5 lun 0: Mar 29 21:16:37 yedi /kernel: st1: Archive Viper 150 is a known rogue For instance, there are devices that respond to all LUNs on a certain target ID, even if they are actually only one device. It is easy to see that the kernel might be fooled into believing that there are 8 LUNs at that particular target ID. The confusion this causes is left as an exercise to the reader. The SCSI subsystem of FreeBSD recognizes devices with bad habits by looking at the INQUIRY response they send when probed. Because the INQUIRY response also includes the version number of the device firmware, it is even possible that for different firmware versions different workarounds are used. See e.g. /sys/scsi/st.c and /sys/scsi/scsiconf.c for more info on how this is done. This scheme works fine, but keep in mind that it of course only works for devices that are KNOWN to be weird. If you are the first to connect your bogus Mumbletech SCSI CDROM you might be the one that has to define which workaround is needed. After you got your Mumbletech working, please send the required workaround to the FreeBSD development team for inclusion in the next release of FreeBSD. Other Mumbletech owners will be grateful to you. Multiple LUN devices

In some cases you come across devices that use multiple logical units (LUNs) on a single SCSI ID. In most cases FreeBSD only probes devices for LUN 0. An example are so called bridge boards that connect 2 non-SCSI harddisks to a SCSI bus (e.g. an Emulex MD21 found in old Sun systems). This means that any devices with LUNs != 0 are not normally found during device probe on system boot. To work around this problem you must add an appropriate entry in /sys/scsi/scsiconf.c and rebuild your kernel. Look for a struct that is initialised like below: { T_DIRECT, T_FIXED, "MAXTOR", "XT-4170S", "B5A", "mx1", SC_ONE_LU } For you Mumbletech BRIDGE2000 that has more than one LUN, acts as a SCSI disk and has firmware revision 123 you would add something like: { T_DIRECT, T_FIXED, "MUMBLETECH", "BRIDGE2000", "123", "sd", SC_MORE_LUS } The kernel on boot scans the inquiry data it receives against the table and acts accordingly. See the source for more info. Tagged command queueing

Modern SCSI devices, particularly magnetic disks, support what is called tagged command queuing (TCQ). In a nutshell, TCQ allows the device to have multiple I/O requests outstanding at the same time. Because the device is intelligent, it can optimise its operations (like head positioning) based on its own request queue. On SCSI devices like RAID (Redundant Array of Independent Disks) arrays the TCQ function is indispensable to take advantage of the device's inherent parallelism. Each I/O request is uniquely identified by a 'tag' (hence the name tagged command queuing) and this tag is used by FreeBSD to see which I/O in the device drivers queue is reported as complete by the device. It should be noted however that TCQ requires device driver support and that some devices implemented it 'not quite right' in their firmware. This problem bit me once, and it leads to highly mysterious problems. In such cases, try to disable TCQ. Busmaster host adapters

Most, but not all, SCSI host adapters are bus mastering controllers. This means that they can do I/O on their own without putting load onto the host CPU for data movement. This is of course an advantage for a multitasking operating system like FreeBSD. It must be noted however that there might be some rough edges. For instance an Adaptec 1542 controller can be set to use different transfer speeds on the host bus (ISA or AT in this case). The controller is settable to different rates because not all motherboards can handle the higher speeds. Problems like hangups, bad data etc might be the result of using a higher data transfer rate then your motherboard can stomach. The solution is of course obvious: switch to a lower data transfer rate and try if that works better. In the case of a Adaptec 1542, there is an option that can be put into the kernel config file to allow dynamic determination of the right, read: fastest feasible, transfer rate. This option is disabled by default: options "TUNE_1542" #dynamic tune of bus DMA speed Check the man pages for the host adapter that you use. Or better still, use the ultimate documentation (read: driver source). Tracking down problems

The following list is an attempt to give a guideline for the most common SCSI problems and their solutions. It is by no means complete. Check for loose connectors and cables. Check and double check the location and number of your terminators. Check if your bus has at least one supplier of terminator power (especially with external terminators. Check if no double target IDs are used. Check if all devices to be used are powered up. Make a minimal bus config with as little devices as possible. If possible, configure your host adapter to use slow bus speeds. Disable tagged command queuing to make things as simple as possible (for a NCR hostadapter based system see man ncrcontrol) If you can compile a kernel, make one with the SCSIDEBUG option, and try accessing the device with debugging turned on for that device. If your device does not even probe at startup, you may have to define the address of the device that is failing, and the desired debug level in /sys/scsi/scsidebug.h. If it probes but just does not work, you can use the scsi(8) command to dynamically set a debug level to it in a running kernel (if SCSIDEBUG is defined). This will give you COPIOUS debugging output with which to confuse the gurus. see man 4 scsi for more exact information. Also look at man 8 scsi. Further reading

If you intend to do some serious SCSI hacking, you might want to have the official standard at hand: Approved American National Standards can be purchased from ANSI at 11 West 42nd Street, 13th Floor, New York, NY 10036, Sales Dept: (212) 642-4900. You can also buy many ANSI standards and most committee draft documents from Global Engineering Documents, 15 Inverness Way East, Englewood, CO 80112-5704, Phone: (800) 854-7179, Outside USA and Canada: (303) 792-2181, FAX: (303) 792- 2192. Many X3T10 draft documents are available electronically on the SCSI BBS (719-574-0424) and on the ncrinfo.ncr.com anonymous ftp site. Latest X3T10 committee documents are: AT Attachment (ATA or IDE) [X3.221-1994] (Approved) ATA Extensions (ATA-2) [X3T10/948D Rev 2i] Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991] (Approved) Small Computer System Interface - 2 (SCSI-2) [X3.131-1994] (Approved) SCSI-2 Common Access Method Transport and SCSI Interface Module (CAM) [X3T10/792D Rev 11] Other publications that might provide you with additional information are: "SCSI: Understanding the Small Computer System Interface", written by NCR Corporation. Available from: Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937 ISBN 0-13-796855-8 "Basics of SCSI", a SCSI tutorial written by Ancot Corporation Contact Ancot for availability information at: Phone: (415) 322-5322 Fax: (415) 322-0455 "SCSI Interconnection Guide Book", an AMP publication (dated 4/93, Catalog 65237) that lists the various SCSI connectors and suggests cabling schemes. Available from AMP at (800) 522-6752 or (717) 564-0100 "Fast Track to SCSI", A Product Guide written by Fujitsu. Available from: Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937 ISBN 0-13-307000-X "The SCSI Bench Reference", "The SCSI Encyclopedia", and the "SCSI Tutor", ENDL Publications, 14426 Black Walnut Court, Saratoga CA, 95070 Phone: (408) 867-6642 "Zadian SCSI Navigator" (quick ref. book) and "Discover the Power of SCSI" (First book along with a one-hour video and tutorial book), Zadian Software, Suite 214, 1210 S. Bascom Ave., San Jose, CA 92128, (408) 293-0800 On Usenet the newsgroups and are noteworthy places to look for more info. You can also find the SCSI-Faq there, which is posted periodically. Most major SCSI device and host adapter suppliers operate ftp sites and/or BBS systems. They may be valuable sources of information about the devices you own.