diff --git a/en_US.ISO8859-1/books/handbook/backups/chapter.sgml b/en_US.ISO8859-1/books/handbook/backups/chapter.sgml index c6ee2e7062..968396b48a 100644 --- a/en_US.ISO8859-1/books/handbook/backups/chapter.sgml +++ b/en_US.ISO8859-1/books/handbook/backups/chapter.sgml @@ -1,719 +1,707 @@ Backups Synopsis The following chapter will cover methods of backing up data, and the programs used to create those backups. If you would like to contribute something to this section, send it to the &a.doc;. Tape Media The major tape media are the 4mm, 8mm, QIC, mini-cartridge and DLT. 4mm (DDS: Digital Data Storage) 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. The DDS-3 standard now supports tape capacities up to 12GB (or 24GB compressed). 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 (Exabyte) 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. The Exabyte “Mammoth” model supports 12GB on one tape (24MB with compression) and costs approximately twice as much as conventional tape drives. 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 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). Mini-cartridges, 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. - - * Mini-Cartridge - - - - DLT 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. With compression, DLT Type IV format supports up to 70GB capacity. 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. AIT AIT is a new format from Sony, and can hold up to 50GB (with compression) per tape. The tapes contain memory chips which retain an index of the tape's contents. This index can be rapidly read by the tape drive to determine the position of files on the tape, instead of the several minutes that would be required for other tapes. Software such as SAMS:Alexandria can operate forty or more AIT tape libraries, communicating directly with the tape's memory chip to display the contents on screen, determine what files where backed up to which tape, locate the correct tape, load it, and restore the data from the tape. Libraries like this cost in the region of $20,000, pricing them a little out of the hobbyist market. 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: sa0(ncr1:4:0): NOT READY asc:4,1 sa0(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 &man.dump.8; data to the tape. &man.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 &man.dump.8;, &man.tar.1;, and &man.cpio.1;. Dump and Restore &man.dump.8; and &man.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. &man.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 &man.ln.1; or mounting one filesystem onto another. &man.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. &man.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. &man.rdump.8; and &man.rrestore.8; backup data across the network to a tape drive attached to another computer. Both programs rely upon &man.rcmd.3; and &man.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 &man.rdump.8; and &man.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/nrsa8 /dev/rda0a 2>&1) Beware: there are security implications to allowing rhosts commands. Evaluate your situation carefully. Tar &man.tar.1; also dates back to Version 6 of ATT Unix (circa 1975). &man.tar.1; operates in cooperation with the filesystem; &man.tar.1; writes files and directories to tape. &man.tar.1; does not support the full range of options that are available from &man.cpio.1;, but &man.tar.1; does not require the unusual command pipeline that &man.cpio.1; uses. Most versions of &man.tar.1; do not support backups across the network. The GNU version of &man.tar.1;, which FreeBSD utilizes, supports remote devices using the same syntax as &man.rdump.8;. To &man.tar.1; to an Exabyte tape drive connected to a Sun called komodo, use: /usr/bin/tar cf komodo:/dev/nrsa8 . 2>&1. For versions without remote device support, you can use a pipeline and &man.rsh.1; to send the data to a remote tape drive. (XXX add an example command) Cpio &man.cpio.1; is the original Unix file interchange tape program for magnetic media. &man.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 &man.cpio.1; and excellent choice for installation media. &man.cpio.1; does not know how to walk the directory tree and a list of files must be provided through stdin. &man.cpio.1; does not support backups across the network. You can use a pipeline and &man.rsh.1; to send the data to a remote tape drive. (XXX add an example command) Pax &man.pax.1; is IEEE/POSIX's answer to &man.tar.1; and &man.cpio.1;. Over the years the various versions of &man.tar.1; and &man.cpio.1; have gotten slightly incompatible. So rather than fight it out to fully standardize them, POSIX created a new archive utility. &man.pax.1; attempts to read and write many of the various &man.cpio.1; and &man.tar.1; formats, plus new formats of its own. Its command set more resembles &man.cpio.1; than &man.tar.1;. Amanda 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? &man.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 &man.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 unwritable 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. See torture-testing Backup and Archive Programs. 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 da0 | lpr), your filesystem table (/etc/fstab) and all boot messages, two copies of each. Second, determine that 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: &man.fdisk.8;, &man.disklabel.8;, &man.newfs.8;, &man.mount.8;, and whichever backup program you use. These programs must be statically linked. If you use &man.dump.8;, the floppy must contain &man.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/rsa0, you might accidently type tar cvf /dev/rsa0 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: /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 da0 ./MAKEDEV da1 ./MAKEDEV da2 ./MAKEDEV sa0 ./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 &man.mount.8; (e.g. mount /dev/da0a /mnt) the root partition of your first disk. If the disklabel was damaged, use &man.disklabel.8; to re-partition and label the disk to match the label that your printed and saved. Use &man.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/sa0). 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? - - - What about backups to floppies? Can I use floppies for backing up my data? Floppy disks are not really a suitable media for making backups as: The media is unreliable, especially over long periods of time Backing up and restoring is very slow They have a very limited capacity (the days of backing up an entire hard disk onto a dozen or so floppies has long since passed). However, if you have no other method of backing up your data then floppy disks are better than no backup at all. If you do have to use floppy disks then ensure that you use good quality ones. Floppies that have been lying around the office for a couple of years are a bad choice. Ideally use new ones from a reputable manufacturer. So how do I backup my data to floppies? The best way to backup to floppy disk is to use &man.tar.1; with the (multi volume) option, which allows backups to span multiple floppies. To backup all the files in the current directory and sub-directory use this (as root): &prompt.root; tar Mcvf /dev/rfd0 * When the first floppy is full &man.tar.1; will prompt you to insert the next volume (because &man.tar.1; is media independent it refers to volumes. In this context it means floppy disk) Prepare volume #2 for /dev/rfd0 and hit return: This is repeated (with the volume number incrementing) until all the specified files have been archived. Can I compress my backups? Unfortunately, &man.tar.1; will not allow the option to be used for multi-volume archives. You could, of course, &man.gzip.1; all the files, &man.tar.1; them to the floppies, then &man.gunzip.1; the files again! How do I restore my backups? To restore the entire archive use: &prompt.root; tar Mxvf /dev/rfd0 To restore only specific files you can either start with the first floppy and use: &prompt.root; tar Mxvf /dev/rfd0 filename &man.tar.1; will prompt you to insert subsequent floppies until it finds the required file. Alternatively, if you know which floppy the file is on then you can simply insert that floppy and use the same command as above. Note that if the first file on the floppy is a continuation from the previous one then &man.tar.1; will warn you that it cannot restore it, even if you have not asked it to! diff --git a/en_US.ISO_8859-1/books/handbook/backups/chapter.sgml b/en_US.ISO_8859-1/books/handbook/backups/chapter.sgml index c6ee2e7062..968396b48a 100644 --- a/en_US.ISO_8859-1/books/handbook/backups/chapter.sgml +++ b/en_US.ISO_8859-1/books/handbook/backups/chapter.sgml @@ -1,719 +1,707 @@ Backups Synopsis The following chapter will cover methods of backing up data, and the programs used to create those backups. If you would like to contribute something to this section, send it to the &a.doc;. Tape Media The major tape media are the 4mm, 8mm, QIC, mini-cartridge and DLT. 4mm (DDS: Digital Data Storage) 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. The DDS-3 standard now supports tape capacities up to 12GB (or 24GB compressed). 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 (Exabyte) 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. The Exabyte “Mammoth” model supports 12GB on one tape (24MB with compression) and costs approximately twice as much as conventional tape drives. 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 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). Mini-cartridges, 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. - - * Mini-Cartridge - - - - DLT 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. With compression, DLT Type IV format supports up to 70GB capacity. 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. AIT AIT is a new format from Sony, and can hold up to 50GB (with compression) per tape. The tapes contain memory chips which retain an index of the tape's contents. This index can be rapidly read by the tape drive to determine the position of files on the tape, instead of the several minutes that would be required for other tapes. Software such as SAMS:Alexandria can operate forty or more AIT tape libraries, communicating directly with the tape's memory chip to display the contents on screen, determine what files where backed up to which tape, locate the correct tape, load it, and restore the data from the tape. Libraries like this cost in the region of $20,000, pricing them a little out of the hobbyist market. 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: sa0(ncr1:4:0): NOT READY asc:4,1 sa0(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 &man.dump.8; data to the tape. &man.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 &man.dump.8;, &man.tar.1;, and &man.cpio.1;. Dump and Restore &man.dump.8; and &man.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. &man.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 &man.ln.1; or mounting one filesystem onto another. &man.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. &man.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. &man.rdump.8; and &man.rrestore.8; backup data across the network to a tape drive attached to another computer. Both programs rely upon &man.rcmd.3; and &man.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 &man.rdump.8; and &man.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/nrsa8 /dev/rda0a 2>&1) Beware: there are security implications to allowing rhosts commands. Evaluate your situation carefully. Tar &man.tar.1; also dates back to Version 6 of ATT Unix (circa 1975). &man.tar.1; operates in cooperation with the filesystem; &man.tar.1; writes files and directories to tape. &man.tar.1; does not support the full range of options that are available from &man.cpio.1;, but &man.tar.1; does not require the unusual command pipeline that &man.cpio.1; uses. Most versions of &man.tar.1; do not support backups across the network. The GNU version of &man.tar.1;, which FreeBSD utilizes, supports remote devices using the same syntax as &man.rdump.8;. To &man.tar.1; to an Exabyte tape drive connected to a Sun called komodo, use: /usr/bin/tar cf komodo:/dev/nrsa8 . 2>&1. For versions without remote device support, you can use a pipeline and &man.rsh.1; to send the data to a remote tape drive. (XXX add an example command) Cpio &man.cpio.1; is the original Unix file interchange tape program for magnetic media. &man.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 &man.cpio.1; and excellent choice for installation media. &man.cpio.1; does not know how to walk the directory tree and a list of files must be provided through stdin. &man.cpio.1; does not support backups across the network. You can use a pipeline and &man.rsh.1; to send the data to a remote tape drive. (XXX add an example command) Pax &man.pax.1; is IEEE/POSIX's answer to &man.tar.1; and &man.cpio.1;. Over the years the various versions of &man.tar.1; and &man.cpio.1; have gotten slightly incompatible. So rather than fight it out to fully standardize them, POSIX created a new archive utility. &man.pax.1; attempts to read and write many of the various &man.cpio.1; and &man.tar.1; formats, plus new formats of its own. Its command set more resembles &man.cpio.1; than &man.tar.1;. Amanda 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? &man.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 &man.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 unwritable 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. See torture-testing Backup and Archive Programs. 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 da0 | lpr), your filesystem table (/etc/fstab) and all boot messages, two copies of each. Second, determine that 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: &man.fdisk.8;, &man.disklabel.8;, &man.newfs.8;, &man.mount.8;, and whichever backup program you use. These programs must be statically linked. If you use &man.dump.8;, the floppy must contain &man.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/rsa0, you might accidently type tar cvf /dev/rsa0 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: /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 da0 ./MAKEDEV da1 ./MAKEDEV da2 ./MAKEDEV sa0 ./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 &man.mount.8; (e.g. mount /dev/da0a /mnt) the root partition of your first disk. If the disklabel was damaged, use &man.disklabel.8; to re-partition and label the disk to match the label that your printed and saved. Use &man.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/sa0). 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? - - - What about backups to floppies? Can I use floppies for backing up my data? Floppy disks are not really a suitable media for making backups as: The media is unreliable, especially over long periods of time Backing up and restoring is very slow They have a very limited capacity (the days of backing up an entire hard disk onto a dozen or so floppies has long since passed). However, if you have no other method of backing up your data then floppy disks are better than no backup at all. If you do have to use floppy disks then ensure that you use good quality ones. Floppies that have been lying around the office for a couple of years are a bad choice. Ideally use new ones from a reputable manufacturer. So how do I backup my data to floppies? The best way to backup to floppy disk is to use &man.tar.1; with the (multi volume) option, which allows backups to span multiple floppies. To backup all the files in the current directory and sub-directory use this (as root): &prompt.root; tar Mcvf /dev/rfd0 * When the first floppy is full &man.tar.1; will prompt you to insert the next volume (because &man.tar.1; is media independent it refers to volumes. In this context it means floppy disk) Prepare volume #2 for /dev/rfd0 and hit return: This is repeated (with the volume number incrementing) until all the specified files have been archived. Can I compress my backups? Unfortunately, &man.tar.1; will not allow the option to be used for multi-volume archives. You could, of course, &man.gzip.1; all the files, &man.tar.1; them to the floppies, then &man.gunzip.1; the files again! How do I restore my backups? To restore the entire archive use: &prompt.root; tar Mxvf /dev/rfd0 To restore only specific files you can either start with the first floppy and use: &prompt.root; tar Mxvf /dev/rfd0 filename &man.tar.1; will prompt you to insert subsequent floppies until it finds the required file. Alternatively, if you know which floppy the file is on then you can simply insert that floppy and use the same command as above. Note that if the first file on the floppy is a continuation from the previous one then &man.tar.1; will warn you that it cannot restore it, even if you have not asked it to!