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+ + Storage Devices + + + + Wilko + Bulte + + +
wilko@FreeBSD.org
+ + + + + $FreeBSD$ + + + This article talks about storage devices with FreeBSD. + + + + + Using ESDI hard disks + + Copyright © 1995, &a.wilko;. 24 September + 1995. + + ESDI is an acronym that means Enhanced Small Device + Interface. It is loosely based on the good old ST506/412 + interface originally devised by Seagate Technology, the makers + of the first affordable 5.25" winchester disk. + + The acronym says Enhanced, and rightly so. In the first + place the speed of the interface is higher, 10 or 15 + Mbits/second instead of the 5 Mbits/second of ST412 interfaced + drives. Secondly some higher level commands are added, making + the ESDI interface somewhat 'smarter' to the operating system + driver writers. It is by no means as smart as SCSI by the way. + ESDI is standardized by ANSI. + + Capacities of the drives are boosted by putting more sectors + on each track. Typical is 35 sectors per track, high capacity + drives I have seen were up to 54 sectors/track. + + Although ESDI has been largely obsoleted by IDE and SCSI + interfaces, the availability of free or cheap surplus drives + makes them ideal for low (or now) budget systems. + + + Concepts of ESDI + + + Physical connections + + The ESDI interface uses two cables connected to each drive. + One cable is a 34 pin flat cable edge connector that carries the + command and status signals from the controller to the drive and + vice-versa. The command cable is daisy chained between all the + drives. So, it forms a bus onto which all drives are + connected. + + The second cable is a 20 pin flat cable edge connector that + carries the data to and from the drive. This cable is radially + connected, so each drive has its own direct connection to the + controller. + + To the best of my knowledge PC ESDI controllers are limited to + using a maximum of 2 drives per controller. This is compatibility + feature(?) left over from the WD1003 standard that reserves only a + single bit for device addressing. + + + + Device addressing + + On each command cable a maximum of 7 devices and 1 controller + can be present. To enable the controller to uniquely identify + which drive it addresses, each ESDI device is equipped with + jumpers or switches to select the devices address. + + On PC type controllers the first drive is set to address 0, + the second disk to address 1. Always make + sure you set each disk to an unique address! So, on a + PC with its two drives/controller maximum the first drive is drive + 0, the second is drive 1. + + + + Termination + + The daisy chained command cable (the 34 pin cable remember?) + needs to be terminated at the last drive on the chain. For this + purpose ESDI drives come with a termination resistor network that + can be removed or disabled by a jumper when it is not used. + + So, one and only one drive, the one at + the farthest end of the command cable has its terminator + installed/enabled. The controller automatically terminates the + other end of the cable. Please note that this implies that the + controller must be at one end of the cable and + not in the middle. + + + + + Using ESDI disks with FreeBSD + + Why is ESDI such a pain to get working in the first + place? + + People who tried ESDI disks with FreeBSD are known to have + developed a profound sense of frustration. A combination of factors + works against you to produce effects that are hard to understand + when you have never seen them before. + + This has also led to the popular legend ESDI and FreeBSD is a + plain NO-GO. The following sections try to list all the pitfalls + and solutions. + + + ESDI speed variants + + As briefly mentioned before, ESDI comes in two speed flavors. + The older drives and controllers use a 10 Mbits/second data + transfer rate. Newer stuff uses 15 Mbits/second. + + It is not hard to imagine that 15 Mbits/second drive cause + problems on controllers laid out for 10 Mbits/second. As always, + consult your controller and drive + documentation to see if things match. + + + + Stay on track + + Mainstream ESDI drives use 34 to 36 sectors per track. Most + (older) controllers cannot handle more than this number of + sectors. Newer, higher capacity, drives use higher numbers of + sectors per track. For instance, I own a 670 MB drive that has 54 + sectors per track. + + In my case, the controller could not handle this number of + sectors. It proved to work well except that it only used 35 + sectors on each track. This meant losing a lot of disk + space. + + Once again, check the documentation of your hardware for more + info. Going out-of-spec like in the example might or might not + work. Give it a try or get another more capable + controller. + + + + Hard or soft sectoring + + Most ESDI drives allow hard or soft sectoring to be selected + using a jumper. Hard sectoring means that the drive will produce + a sector pulse on the start of each new sector. The controller + uses this pulse to tell when it should start to write or + read. + + Hard sectoring allows a selection of sector size (normally + 256, 512 or 1024 bytes per formatted sector). FreeBSD uses 512 + byte sectors. The number of sectors per track also varies while + still using the same number of bytes per formatted sector. The + number of unformatted bytes per sector + varies, dependent on your controller it needs more or less + overhead bytes to work correctly. Pushing more sectors on a + track of course gives you more usable space, but might give + problems if your controller needs more bytes than the drive + offers. + + In case of soft sectoring, the controller itself determines + where to start/stop reading or writing. For ESDI hard sectoring + is the default (at least on everything I came across). I never + felt the urge to try soft sectoring. + + In general, experiment with sector settings before you install + FreeBSD because you need to re-run the low-level format after each + change. + + + + Low level formatting + + ESDI drives need to be low level formatted before they are + usable. A reformat is needed whenever you figgle with the number + of sectors/track jumpers or the physical orientation of the drive + (horizontal, vertical). So, first think, then format. The format + time must not be underestimated, for big disks it can take + hours. + + After a low level format, a surface scan is done to find and + flag bad sectors. Most disks have a manufacturer bad block list + listed on a piece of paper or adhesive sticker. In addition, on + most disks the list is also written onto the disk. Please use the + manufacturer's list. It is much easier to remap a defect now than + after FreeBSD is installed. + + Stay away from low-level formatters that mark all sectors of a + track as bad as soon as they find one bad sector. Not only does + this waste space, it also and more importantly causes you grief + with bad144 (see the section on bad144). + + + + Translations + + Translations, although not exclusively a ESDI-only problem, + might give you real trouble. Translations come in multiple + flavors. Most of them have in common that they attempt to work + around the limitations posed upon disk geometries by the original + IBM PC/AT design (thanks IBM!). + + First of all there is the (in)famous 1024 cylinder limit. For + a system to be able to boot, the stuff (whatever operating system) + must be in the first 1024 cylinders of a disk. Only 10 bits are + available to encode the cylinder number. For the number of + sectors the limit is 64 (0-63). When you combine the 1024 + cylinder limit with the 16 head limit (also a design feature) you + max out at fairly limited disk sizes. + + To work around this problem, the manufacturers of ESDI PC + controllers added a BIOS prom extension on their boards. This + BIOS extension handles disk I/O for booting (and for some + operating systems all disk I/O) by using + translation. For instance, a big drive might be presented to the + system as having 32 heads and 64 sectors/track. The result is + that the number of cylinders is reduced to something below 1024 + and is therefore usable by the system without problems. It is + noteworthy to know that FreeBSD does not use the BIOS after its + kernel has started. More on this later. + + A second reason for translations is the fact that most older + system BIOSes could only handle drives with 17 sectors per track + (the old ST412 standard). Newer system BIOSes usually have a + user-defined drive type (in most cases this is drive type + 47). + + + Whatever you do to translations after reading this document, + keep in mind that if you have multiple operating systems on the + same disk, all must use the same translation + + + While on the subject of translations, I have seen one + controller type (but there are probably more like this) offer the + option to logically split a drive in multiple partitions as a BIOS + option. I had select 1 drive == 1 partition because this + controller wrote this info onto the disk. On power-up it read the + info and presented itself to the system based on the info from the + disk. + + + + Spare sectoring + + Most ESDI controllers offer the possibility to remap bad + sectors. During/after the low-level format of the disk bad + sectors are marked as such, and a replacement sector is put in + place (logically of course) of the bad one. + + In most cases the remapping is done by using N-1 sectors on + each track for actual data storage, and sector N itself is the + spare sector. N is the total number of sectors physically + available on the track. The idea behind this is that the + operating system sees a 'perfect' disk without bad sectors. In + the case of FreeBSD this concept is not usable. + + The problem is that the translation from + bad to good is performed + by the BIOS of the ESDI controller. FreeBSD, being a true 32 bit + operating system, does not use the BIOS after it has been booted. + Instead, it has device drivers that talk directly to the + hardware. + + So: don't use spare sectoring, bad block remapping + or whatever it may be called by the controller manufacturer when + you want to use the disk for FreeBSD. + + + + Bad block handling + + The preceding section leaves us with a problem. The + controller's bad block handling is not usable and still FreeBSD's + filesystems assume perfect media without any flaws. To solve this + problem, FreeBSD use the bad144 tool. Bad144 + (named after a Digital Equipment standard for bad block handling) + scans a FreeBSD slice for bad blocks. Having found these bad + blocks, it writes a table with the offending block numbers to the + end of the FreeBSD slice. + + When the disk is in operation, the disk accesses are checked + against the table read from the disk. Whenever a block number is + requested that is in the bad144 list, a + replacement block (also from the end of the FreeBSD slice) is + used. In this way, the bad144 replacement + scheme presents 'perfect' media to the FreeBSD filesystems. + + There are a number of potential pitfalls associated with the + use of bad144. First of all, the slice cannot + have more than 126 bad sectors. If your drive has a high number + of bad sectors, you might need to divide it into multiple FreeBSD + slices each containing less than 126 bad sectors. Stay away from + low-level format programs that mark every + sector of a track as bad when they find a flaw on the track. As + you can imagine, the 126 limit is quickly reached when the + low-level format is done this way. + + Second, if the slice contains the root filesystem, the slice + should be within the 1024 cylinder BIOS limit. During the boot + process the bad144 list is read using the BIOS and this only + succeeds when the list is within the 1024 cylinder limit. + + + The restriction is not that only the root + filesystem must be within the 1024 cylinder + limit, but rather the entire slice that + contains the root filesystem. + + + + + Kernel configuration + + ESDI disks are handled by the same wddriver + as IDE and ST412 MFM disks. The wd driver + should work for all WD1003 compatible interfaces. + + Most hardware is jumperable for one of two different I/O + address ranges and IRQ lines. This allows you to have two wd + type controllers in one system. + + When your hardware allows non-standard strappings, you can use + these with FreeBSD as long as you enter the correct info into the + kernel config file. An example from the kernel config file (they + live in /sys/i386/conf BTW). + + # First WD compatible controller +controller wdc0 at isa? port "IO_WD1" bio irq 14 vector wdintr +disk wd0 at wdc0 drive 0 +disk wd1 at wdc0 drive 1 +# Second WD compatible controller +controller wdc1 at isa? port "IO_WD2" bio irq 15 vector wdintr +disk wd2 at wdc1 drive 0 +disk wd3 at wdc1 drive 1 + + + + + Particulars on ESDI hardware + + + Adaptec 2320 controllers + + I successfully installed FreeBSD onto a ESDI disk controlled + by a ACB-2320. No other operating system was present on the + disk. + + To do so I low level formatted the disk using + NEFMT.EXE (ftpable from + www.adaptec.com) and answered NO to + the question whether the disk should be formatted with a spare + sector on each track. The BIOS on the ACD-2320 was disabled. I + used the free configurable option in the system + BIOS to allow the BIOS to boot it. + + Before using NEFMT.EXE I tried to format + the disk using the ACB-2320 BIOS built-in formatter. This proved + to be a show stopper, because it did not give me an option to + disable spare sectoring. With spare sectoring enabled the FreeBSD + installation process broke down on the bad144 + run. + + Please check carefully which + ACB-232xy variant you have. The + x is either 0 or + 2, indicating a controller without or with a + floppy controller on board. + + The y is more interesting. It can either + be a blank, a A-8 or a D. A + blank indicates a plain 10 Mbits/second controller. An + A-8 indicates a 15 Mbits/second controller + capable of handling 52 sectors/track. A D + means a 15 Mbits/second controller that can also handle drives + with > 36 sectors/track (also 52 ?). + + All variations should be capable of using 1:1 interleaving. + Use 1:1, FreeBSD is fast enough to handle it. + + + + Western Digital WD1007 controllers + + I successfully installed FreeBSD onto a ESDI disk controlled + by a WD1007 controller. To be precise, it was a WD1007-WA2. + Other variations of the WD1007 do exist. + + To get it to work, I had to disable the sector translation and + the WD1007's onboard BIOS. This implied I could not use the + low-level formatter built into this BIOS. Instead, I grabbed + WDFMT.EXE from www.wdc.com Running this formatted my drive + just fine. + + + + Ultrastor U14F controllers + + According to multiple reports from the net, Ultrastor ESDI + boards work OK with FreeBSD. I lack any further info on + particular settings. + + + + + Further reading + + If you intend to do some serious ESDI hacking, you might want to + have the official standard at hand: + + The latest ANSI X3T10 committee document is: Enhanced Small + Device Interface (ESDI) [X3.170-1990/X3.170a-1991] [X3T10/792D + Rev 11] + + On Usenet the newsgroup comp.periphs is a noteworthy place + to look for more info. + + The World Wide Web (WWW) also proves to be a very handy info + source: For info on Adaptec ESDI controllers see http://www.adaptec.com/. For + info on Western Digital controllers see http://www.wdc.com/. + + + + Thanks to... + + Andrew Gordon for sending me an Adaptec 2320 controller and ESDI + disk for testing. + + + + + 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 (approximately 1985) is rapidly becoming obsolete. The + current standard is SCSI-2 (see Further reading), 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 + million transfers per second (20 Mbytes/sec on a 8 bit bus), Fast-40 + is 40 million transfers per second (40 Mbytes/sec on a 8 bit bus). + Most hard drives sold today are single-ended Ultra SCSI (8 or 16 + bits). + + 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 + fibre channel 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 a 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 million transfers/second are also emerging (Fast-20 == Ultra + SCSI and Fast-40 == Ultra2 SCSI). + + + 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 million + transfers/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. + + + 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 Further + reading) 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. Many SCSI devices come 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 single line on the 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. (Note the potential here; + the nastiest part is that it may or may not work.) + + 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. + + + Termination is to be done on a per-line basis. This means + if you have both narrow and wide buses connected to the same + host adapter, you need to enable termination on the higher 8 + bits of the bus on the adapter (as well as the last devices on + each bus, of course). + + + 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 + enabled or disabled 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 are software configurable, using + some sort of setup tool. Some will even auto-detect the cables + attached to the connectors and automatically set up the + termination as necessary. At any rate, consult your + 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. Some SCSI host adapters let you change the target ID + from the boot menu. (Yet some others will not let you change the + ID from 7.) 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 (usually 16). + + + A narrow SCSI device can not communicate with a SCSI device + with a target ID larger than 7. This means it is generally not + a good idea to move your SCSI host adapter's target ID to + something higher than 7 (or your CDROM will stop + working). + + + 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. Note however that the lower 8 + IDs have higher priorities than the higher 8 IDs on a wide-SCSI + bus. Thus, the order of target IDs is: [7 6 .. 1 0 15 14 .. 9 8] + on a wide-SCSI system. (If you are wondering why the lower 8 + have higher priority, read the previous paragraph for a + hint.) + + 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, rings, cobwebs or whatever else people might want to + invent. One of the most common mistakes is for people with + wide-SCSI host adapters to connect devices on all three connecters + (external connector, internal wide connector, internal narrow + connector). Don't do that. It may appear to work if you are + really lucky, but I can almost guarantee that your system will + stop functioning at the most unfortunate moment (this is also + known as Murphy's law). + + You might notice that the terminator issue discussed earlier + becomes rather hairy if your bus is not linear. Also, if you have + more connectors than devices on your internal SCSI cable, make + sure you attach devices on connectors on both ends instead of + using the connectors in the middle and let one or both ends + dangle. This will screw up the termination of the bus. + + 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: <MICROP 1588-15MB1057404HSP4> +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. + + + Note that most of the EISA/PCI drivers (namely + ahb, ahc, + ncr and amd + will automatically obtain the correct parameters from the host + adapters themselves at boot time; thus, you just need to write, + for instance, controller ahc0. + + + An example loosely based on the FreeBSD 2.2.5-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!) +# amd: AMD 53c974 based SCSI cards (e.g., Tekram DC-390 and 390T) +# bt: Most Buslogic controllers +# nca: ProAudioSpectrum cards using the NCR 5380 or Trantor T130 +# ncr: NCR/Symbios 53c810/815/825/875 etc based SCSI cards +# 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/294x/394x etc controller] +controller ahc0 + +[For an NCR/Symbios 53c875 based controller] +controller ncr0 + +[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 ncr0 +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 ncr0] +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 NCR/Symbios 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. + + + 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 e.g., man 4 ahc for info on the + Adaptec 294x 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 + + 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: <TANDBERG TDC 3600 -06:> +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: <ARCHIVE VIPER 150 21247-005> +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 initialized 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 queuing + + 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 optimize 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 + hang-ups, 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 host adapter 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 + &man.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 + +
+ 13th Floor + 11 West 42nd Street + 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 comp.periphs.scsi and comp.periphs 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. + + + + + * Disk/tape controllers + + + * SCSI + + + + + + * IDE + + + + + + * Floppy + + + + + + + Hard drives + + + SCSI hard drives + + Contributed by &a.asami;. 17 February + 1998. + + As mentioned in the SCSI section, + virtually all SCSI hard drives sold today are SCSI-2 compliant and + thus will work fine as long as you connect them to a supported SCSI + host adapter. Most problems people encounter are either due to + badly designed cabling (cable too long, star topology, etc.), + insufficient termination, or defective parts. Please refer to the + SCSI section first if your SCSI hard + drive is not working. However, there are a couple of things you may + want to take into account before you purchase SCSI hard drives for + your system. + + + Rotational speed + + Rotational speeds of SCSI drives sold today range from around + 4,500RPM to 10,000RPM. Most of them are either 5,400RPM or + 7,200RPM. Even though the 7,200RPM drives can generally transfer + data faster, they run considerably hotter than their 5,400RPM + counterparts. A large fraction of today's disk drive malfunctions + are heat-related. If you do not have very good cooling in your PC + case, you may want to stick with 5,400RPM or slower drives. + + Note that newer drives, with higher areal recording densities, + can deliver much more bits per rotation than older ones. Today's + top-of-line 5,400RPM drives can sustain a throughput comparable to + 7,200RPM drives of one or two model generations ago. The number + to find on the spec sheet for bandwidth is internal data + (or transfer) rate. It is usually in megabits/sec so + divide it by 8 and you'll get the rough approximation of how much + megabytes/sec you can get out of the drive. + + (If you are a speed maniac and want a 10,000RPM drive for your + cute little PC, be my guest; however, those drives become + extremely hot. Don't even think about it if you don't have a fan + blowing air directly at the drive or a + properly ventilated disk enclosure.) + + Obviously, the latest 10,000RPM drives and 7,200RPM drives can + deliver more data than the latest 5,400RPM drives, so if absolute + bandwidth is the necessity for your applications, you have little + choice but to get the faster drives. Also, if you need low + latency, faster drives are better; not only do they usually have + lower average seek times, but also the rotational delay is one + place where slow-spinning drives can never beat a faster one. + (The average rotational latency is half the time it takes to + rotate the drive once; thus, it's 3 milliseconds for 10,000RPM + drives, 4.2ms for 7,200RPM drives and 5.6ms for 5,400RPM drives.) + Latency is seek time plus rotational delay. Make sure you + understand whether you need low latency or more accesses per + second, though; in the latter case (e.g., news servers), it may + not be optimal to purchase one big fast drive. You can achieve + similar or even better results by using the ccd (concatenated + disk) driver to create a striped disk array out of multiple slower + drives for comparable overall cost. + + Make sure you have adequate air flow around the drive, + especially if you are going to use a fast-spinning drive. You + generally need at least 1/2" (1.25cm) of spacing above and below a + drive. Understand how the air flows through your PC case. Most + cases have the power supply suck the air out of the back. See + where the air flows in, and put the drive where it will have the + largest volume of cool air flowing around it. You may need to seal + some unwanted holes or add a new fan for effective cooling. + + Another consideration is noise. Many 7,200 or faster drives + generate a high-pitched whine which is quite unpleasant to most + people. That, plus the extra fans often required for cooling, may + make 7,200 or faster drives unsuitable for some office and home + environments. + + + + Form factor + + Most SCSI drives sold today are of 3.5" form factor. They + come in two different heights; 1.6" (half-height) or + 1" (low-profile). The half-height drive is the same + height as a CDROM drive. However, don't forget the spacing rule + mentioned in the previous section. If you have three standard + 3.5" drive bays, you will not be able to put three half-height + drives in there (without frying them, that is). + + + + Interface + + The majority of SCSI hard drives sold today are Ultra or + Ultra-wide SCSI. The maximum bandwidth of Ultra SCSI is 20MB/sec, + and Ultra-wide SCSI is 40MB/sec. There is no difference in max + cable length between Ultra and Ultra-wide; however, the more + devices you have on the same bus, the sooner you will start having + bus integrity problems. Unless you have a well-designed disk + enclosure, it is not easy to make more than 5 or 6 Ultra SCSI + drives work on a single bus. + + On the other hand, if you need to connect many drives, going + for Fast-wide SCSI may not be a bad idea. That will have the same + max bandwidth as Ultra (narrow) SCSI, while electronically it's + much easier to get it right. My advice would be: if + you want to connect many disks, get wide SCSI drives; they usually + cost a little more but it may save you down the road. (Besides, + if you can't afford the cost difference, you shouldn't be building + a disk array.) + + There are two variant of wide SCSI drives; 68-pin and 80-pin + SCA (Single Connector Attach). The SCA drives don't have a + separate 4-pin power connector, and also read the SCSI ID settings + through the 80-pin connector. If you are really serious about + building a large storage system, get SCA drives and a good SCA + enclosure (dual power supply with at least one extra fan). They + are more electronically sound than 68-pin counterparts because + there is no stub of the SCSI bus inside the disk + canister as in arrays built from 68-pin drives. They are easier + to install too (you just need to screw the drive in the canister, + instead of trying to squeeze in your fingers in a tight place to + hook up all the little cables (like the SCSI ID and disk activity + LED lines). + + + + + * IDE hard drives + + + + + + + Tape drives + + Contributed by &a.jmb;. 2 July + 1996. + + + General tape access commands + + &man.mt.1; provides generic access to the tape drives. Some of + the more common commands are rewind, + erase, and status. See the + &man.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 Disk/tape + controllers. + + + + SCSI drives + + The &man.st.4; driver provides support for 8mm (Exabyte), 4mm + (DAT: Digital Audio Tape), QIC (Quarter-Inch Cartridge), DLT + (Digital Linear Tape), QIC Mini cartridge and 9-track (remember the + big reels that you see spinning in Hollywood computer rooms) tape + drives. See the &man.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) + + Archive Python + 28454 + + Archive Python + 04687 + + HP C1533A + + HP C1534A + + HP 35450A + + HP 35470A + + HP 35480A + + SDT-5000 + + Wangtek + 6200 + + + + 8mm (Exabyte) + + EXB-8200 + + EXB-8500 + + EXB-8505 + + + + QIC (Quarter-Inch Cartridge) + + Archive Anaconda + 2750 + + Archive Viper + 60 + + Archive Viper + 150 + + Archive Viper + 2525 + + Tandberg TDC + 3600 + + Tandberg TDC + 3620 + + Tandberg TDC + 3800 + + Tandberg TDC + 4222 + + Wangtek + 5525ES + + + + DLT (Digital Linear Tape) + + Digital TZ87 + + + + Mini-Cartridge + + Conner CTMS + 3200 + + Exabyte 2501 + + + + Autoloaders/Changers + + Hewlett-Packard HP C1553A + Autoloading DDS2 + + + + + * IDE drives + + + + + + Floppy drives + + Conner 420R + + + + * Parallel port drives + + + + + + Detailed Information + + + Archive Anaconda 2750 + + 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 &man.dump.8;. + Rates of 530kB/s have been reported when using + Amanda + + 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; + + + + Archive Python 28454 + + 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 + 595-3067. + + Reported by: Bob Bishop rb@gid.co.uk + + Throughput is in the 1.5 MByte/sec range, however this will + drop if the disks and tape drive are on the same SCSI + controller. + + Reported by: Robert E. Seastrom + rs@seastrom.com + + + + Archive Python 04687 + + The boot message identifier for this drive is ARCHIVE + Python 04687-XXX 6580 Removable Sequential + Access SCSI-2 device + + This is a DAT-DDS-2 drive. + + Native capacity is 4GB when using 120m tapes. + + This drive supports hardware data compression. Switch 4 + controls MRS (Media Recognition System). MRS tapes have stripes + on the transparent leader. Switch 4 off + enables MRS, on disables MRS. + + Parity is controlled by switch 5. Switch 5 + on to enable parity control. Compression is + enabled with Switch 6 off. It is possible to + override compression with the SCSI MODE SELECT + command (see &man.mt.1;). + + Data transfer rate is 800kB/s. + + + + Archive Viper 60 + + 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 + + + + Archive Viper 150 + + 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 (&man.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 + + &a.msmith; + + + + Archive Viper 2525 + + 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. + + + + Conner 420R + + The boot message identifier for this drive is Conner + tape. + + This is a floppy controller, mini cartridge 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 + + + + Conner CTMS 3200 + + The boot message identifier for this drive is CONNER + CTMS 3200 7.00 type 1 removable SCSI + 2. + + This is a mini cartridge 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 + + + + <ulink + url="http://www.digital.com/info/Customer-Update/931206004.txt.html">DEC TZ87</ulink> + + 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; + + + + <ulink + url="http://www.Exabyte.COM:80/Products/Minicartridge/2501/Rfeatures.html">Exabyte EXB-2501</ulink> + + 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 + mini cartridges. + + Data transfer rate is XXX + + This drive can read and write DC2300 (550MB), DC2750 (750MB), + MC3000 (750MB), and MC3000XL (1GB) mini cartridges. + + 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 + + &prompt.root; mt -f /dev/st0ctl.0 blocksize 1024 + + Before using a mini cartridge for the first time, the + mini cartridge must be formated. FreeBSD 2.1.0-RELEASE and + earlier: + + &prompt.root; /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: + + &prompt.root; /sbin/scsiformat -q -w /dev/rst0.ctl + + Right now, this drive cannot really be recommended for + FreeBSD. + + Reported by: Bob Beaulieu + ez@eztravel.com + + + + Exabyte EXB-8200 + + 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: &a.msmith; + + + + Exabyte EXB-8500 + + 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 + + + + <ulink + url="http://www.Exabyte.COM:80/Products/8mm/8505XL/Rfeatures.html">Exabyte EXB-8505</ulink> + + 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 + + + + Hewlett-Packard HP C1533A + + 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 + switch 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, with host + control + + + + 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 HP + SureStore Tape Products and Hewlett-Packard + Disk and Tape Technical Information 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; + + + + Hewlett-Packard HP 1534A + + 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 + 2000i + 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 + + + + Hewlett-Packard HP C1553A Autoloading DDS2 + + The boot message identifier for this drive is "". + + This is a DDS-2 tape drive with a tape changer. 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 12000e + 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" + + + + Hewlett-Packard HP 35450A + + 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 + + + + Hewlett-Packard HP 35470A + + 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 + 2000i + 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) + + + + + Hewlett-Packard HP 35480A + + 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 HP C1533A for the proper + switch settings. + + Data transfer rate is 183kB/s. + + This drive is used in Hewlett-Packard's SureStore 5000eU and + 5000i + 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. + + + + <ulink + url="http://www.sel.sony.com/SEL/ccpg/storage/tape/t5000.html">Sony SDT-5000</ulink> + + 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; + + + + Tandberg TDC 3600 + + 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 (&man.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: &a.msmith; + + + + Tandberg TDC 3620 + + This is very similar to the Tandberg TDC 3600 + drive. + + Reported by: &a.joerg; + + + + Tandberg TDC 3800 + + The boot message identifier for this drive is + TANDBERG TDC 3800 =04Y Removable + Sequential Access SCSI-2 device + + This is a QIC tape drive. + + Native capacity is 525MB. + + Reported by: &a.jhs; + + + + Tandberg TDC 4222 + + 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 (&man.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; + + + + Wangtek 5525ES + + 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 (&man.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 + + + + Wangtek 6200 + + 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 + + + + + + + CDROM drives + + Contributed by &a.obrien;. 23 November + 1997. + + 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 controllable by the various + audio player software. + + Another area where SCSI CDROM manufacturers are cutting corners is + adherence to the SCSI + specification. Many SCSI CDROMs will respond to multiple LUNs for its target + address. Known violators include the 6x Teac CD-56S 1.0D. + + +
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