570 lines
22 KiB
Text
570 lines
22 KiB
Text
<!-- $Id: backups.sgml,v 1.1 1998-04-30 10:31:01 obrien Exp $ -->
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<!-- The FreeBSD Documentation Project -->
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<!--
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<!DOCTYPE chapt PUBLIC "-//FreeBSD//DTD linuxdoc//EN"> -->
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<chapt><heading>Backups<label id="backups"></heading>
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<p>Issues of hardware compatibility are among the most
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troublesome in the computer industry today and FreeBSD is by
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no means immune to trouble. In this respect, FreeBSD's
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advantage of being able to run on inexpensive commodity PC
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hardware is also its liability when it comes to support for
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the amazing variety of components on the market. While it
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would be impossible to provide a exhaustive listing of
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hardware that FreeBSD supports, this section serves as a
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catalog of the device drivers included with FreeBSD and the
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hardware each drivers supports. Where possible and
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appropriate, notes about specific products are included.
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You may also want to refer to <ref id="kernelconfig:config"
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name="the kernel configuration file"> section in this handbook for
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a list of supported devices.
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As FreeBSD is a volunteer project without a funded testing
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department, we depend on you, the user, for much of the
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information contained in this catalog. If you have direct
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experience of hardware that does or does not work with
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FreeBSD, please let us know by sending e-mail to the &a.doc;.
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Questions about supported hardware
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should be directed to the &a.questions (see
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<ref id="eresources:mail" name="Mailing Lists"> for more
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information). When submitting information or asking a
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question, please remember to specify exactly what version of
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FreeBSD you are using and include as many details of your
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hardware as possible.
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<sect><heading>* What about backups to floppies?</heading>
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<sect><heading> Tape Media<label id="backups:tapebackups"></heading>
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<p>The major tape media are the 4mm, 8mm, QIC, mini-cartridge and
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DLT.
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<sect1><heading> 4mm (DDS: Digital Data Storage)
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<label id="backups:tapebackups:4mm"></heading>
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<!--gen-->
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<p>4mm tapes are replacing QIC as the workstation backup
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media of choice. This trend accelerated greatly when Conner
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purchased Archive, a leading manufacturer of QIC drives, and then
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stopped production of QIC drives. 4mm drives are small and quiet
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but do not have the reputation for reliability that is enjoyed by 8mm drives.
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The cartridges are less expensive and smaller (3 x 2 x 0.5
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inches, 76 x 51 x 12 mm) than 8mm cartridges. 4mm, like 8mm, has
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comparatively short head life for the same reason, both use
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helical scan.
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<!--spec-->
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<p>Data thruput on these drives starts ~150kB/s, peaking
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at ~500kB/s. Data capacity starts at 1.3 GB and ends at 2.0 GB.
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Hardware compression, available with most of these drives,
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approximately doubles the capacity. Multi-drive tape library
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units can have 6 drives in a single cabinet with automatic tape
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changing. Library capacities reach 240 GB.
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<!--tech-->
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<p>4mm drives, like 8mm drives, use helical-scan. All
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the benefits and drawbacks of helical-scan apply to both 4mm and
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8mm drives.
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<p>Tapes should be retired from use after 2,000 passes or
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100 full backups.
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<sect1><heading> 8mm (Exabyte)<label id="backups:tapebackups:8mm">
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</heading>
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<!--gen-->
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<p>8mm tapes are the most common SCSI tape drives; they
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are the best choice of exchanging tapes. Nearly every site has
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an exabyte 2 GB 8mm tape drive. 8mm drives are reliable,
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convenient and quiet. Cartridges are inexpensive and small (4.8 x
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3.3 x 0.6 inches; 122 x 84 x 15 mm). One downside of 8mm tape is
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relatively short head and tape life due to the high rate of
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relative motion of the tape across the heads.
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<!--spec-->
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<p>Data thruput ranges from ~250kB/s to ~500kB/s. Data
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sizes start at 300 MB and go up to 7 GB. Hardware compression,
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available with most of these drives, approximately doubles the
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capacity. These drives are available as single units or
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multi-drive tape libraries with 6 drives and 120 tapes in a
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single cabinet. Tapes are changed automatically by the unit.
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Library capacities reach 840+ GB.
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<!--tech-->
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<p>Data is recorded onto the tape using helical-scan, the
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heads are positioned at an angle to the media (approximately 6
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degrees). The tape wraps around 270 degrees of the spool that
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holds the heads. The spool spins while the tape slides over the
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spool. The result is a high density of data and closely packed
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tracks that angle across the tape from one edge to the other.
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<sect1><heading> QIC<label id="backups:tapebackups:qic"></heading>
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<!--gen-->
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<p>QIC-150 tapes and drives are, perhaps, the most common
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tape drive and media around. QIC tape drives are the least
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expensive "serious" backup drives. The downside is the cost of
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media. QIC tapes are expensive compared to 8mm or 4mm tapes, up
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to 5 times the price per GB data storage. But, if your needs can
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be satisfied with a half-dozen tapes, QIC may be the correct
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choice. QIC is the <em>most</em> common tape drive. Every site
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has a QIC drive of some density or another. Therein lies the
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rub, QIC has a large number of densities on physically similar
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(sometimes identical) tapes. QIC drives are not quiet. These
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drives audibly seek before they begin to record data and are
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clearly audible whenever reading, writing or seeking. QIC tapes
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measure (6 x 4 x 0.7 inches; 15.2 x 10.2 x 1.7 mm). <ref
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id="backups:tapebackups:mini" name="Mini-cartridges">, which also
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use 1/4" wide tape are discussed separately. Tape libraries and
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changers are not available.
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<!--spec-->
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<p>Data thruput ranges from ~150kB/s to ~500kB/s. Data
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capacity ranges from 40 MB to 15 GB. Hardware compression is
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available on many of the newer QIC drives. QIC drives are less
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frequently installed; they are being supplanted by DAT drives.
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<!--tech-->
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<p>Data is recorded onto the tape in tracks. The tracks
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run along the long axis of the tape media from one end to the
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other. The number of tracks, and therefore the width of a track,
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varies with the tape's capacity. Most if not all newer drives
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provide backward-compatibility at least for reading (but often
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also for writing). QIC has a good reputation regarding the
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safety of the data (the mechanics are simpler and more robust
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than for helical scan drives).
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<p>Tapes should be retired from use after 5,000 backups.
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<sect1><heading> * Mini-Cartridge<label id="backups:tapebackups:mini">
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</heading>
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<sect1><heading> DLT<label id="backups:tapebackups:dlt"></heading>
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<!--gen-->
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<p>DLT has the fastest data transfer rate of all the drive
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types listed here. The 1/2" (12.5mm) tape is contained in a
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single spool cartridge (4 x 4 x 1 inches; 100 x 100 x 25 mm). The
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cartridge has a swinging gate along one entire side of the
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cartridge. The drive mechanism opens this gate to extract the
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tape leader. The tape leader has an oval hole in it which the
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drive uses to "hook" the tape. The take-up spool is located
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inside the tape drive. All the other tape cartridges listed here
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(9 track tapes are the only exception) have both the supply and
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take-up spools located inside the tape cartridge itself.
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<!--spec-->
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Data thruput is approximately 1.5MB/s, three times the
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thruput of 4mm, 8mm, or QIC tape drives. Data capacities range
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from 10GB to 20GB for a single drive. Drives are available in
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both multi-tape changers and multi-tape, multi-drive tape
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libraries containing from 5 to 900 tapes over 1 to 20 drives,
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providing from 50GB to 9TB of storage.
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<!--tech-->
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Data is recorded onto the tape in tracks parallel to the
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direction of travel (just like QIC tapes). Two tracks are written
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at once. Read/write head lifetimes are relatively long; once the
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tape stops moving, there is no relative motion between the heads
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and the tape.
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<sect1><heading> Using a new tape for the first time</heading>
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<p>The first time that you try to read or write a new,
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completely blank tape, the operation will fail. The console
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messages should be similar to:
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<tscreen><verb>
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st0(ncr1:4:0): NOT READY asc:4,1
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st0(ncr1:4:0): Logical unit is in process of becoming ready
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</verb></tscreen>
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The tape does not contain an Identifier Block (block number
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0). All QIC tape drives since the adoption of QIC-525 standard
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write an Identifier Block to the tape. There are two
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solutions:
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<p><tt>mt fsf 1</tt> causes the tape drive to write an
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Identifier Block to the tape.
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<p>Use the front panel button to eject the tape.
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<p>Re-insert the tape and <tt>dump(8)</tt> data to the
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tape.
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<p><tt>dump(8)</tt> will report <tt>DUMP: End of tape
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detected</tt> and the console will show: <tt>HARDWARE FAILURE
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info:280 asc:80,96</tt>
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<p>rewind the tape using: <tt>mt rewind</tt>
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<p>Subsequent tape operations are successful.
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<sect><heading> Backup Programs<label id="backup:programs"></heading>
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<p>The three major programs are <tt>dump(8)</tt>,
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<tt>tar(1)</tt>, and <tt>cpio(1)</tt>.
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<sect1><heading> Dump and Restore</heading>
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<!--gen-->
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<p><tt>dump(8)</tt> and <tt>restore(8)</tt> are the
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traditional Unix backup programs. They operate on the drive as a
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collection of disk blocks, below the abstractions of files, links
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and directories that are created by the filesystems.
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<tt>dump(8)</tt> backs up devices, entire filesystems, not parts
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of a filesystem and not directory trees that span more than one
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filesystem, using either soft links <tt>ln(1)</tt> or mounting
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one filesystem onto another. <tt>dump(8)</tt> does not write
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files and directories to tape, but rather writes the data blocks
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that are the building blocks of files and directories.
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<tt>dump(8)</tt> has quirks that remain from its early days in
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Version 6 of ATT Unix (circa 1975). The default parameters are
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suitable for 9-track tapes (6250 bpi), not the high-density media
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available today (up to 62,182 ftpi). These defaults must be
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overridden on the command line to utilize the capacity of current
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tape drives.
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<p><tt>rdump(8)</tt> and <tt>rrestore(8)</tt> backup data
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across the network to a tape drive attached to another computer.
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Both programs rely upon <tt>rcmd(3)</tt> and <tt>ruserok(3)</tt>
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to access the remote tape drive. Therefore, the user performing
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the backup must have <tt>rhosts</tt> access to the remote
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computer. The arguments to <tt>rdump(8)</tt> and
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<tt>rrestore(8)</tt> must suitable to use on the remote computer.
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(e.g. When <tt>rdump</tt>'ing from a FreeBSD computer to an
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Exabyte tape drive connected to a Sun called komodo, use: <tt>/sbin/rdump
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0dsbfu 54000 13000 126 komodo:/dev/nrst8 /dev/rsd0a 2>&1</tt>)
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Beware: there are security implications to allowing
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<tt>rhosts</tt> commands. Evaluate your situation carefully.
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<sect1><heading> Tar</heading>
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<!--gen-->
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<p><tt>tar(1)</tt> also dates back to Version 6 of ATT
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Unix (circa 1975). <tt>tar(1)</tt> operates in cooperation with
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the filesystem; <tt>tar(1)</tt> writes files and directories to
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tape. <tt>tar(1)</tt> does not support the full range of options
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that are available from <tt>cpio(1)</tt>, but <tt>tar(1)</tt>
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does not require the unusual command pipeline that
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<tt>cpio(1)</tt> uses.
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<p>Most versions of <tt>tar(1)</tt> do not support backups across the
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network. The GNU version of <tt>tar(1)</tt>, which FreeBSD utilizes, supports
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remote devices using the same syntax as <tt>rdump</tt>. To <tt>tar(1)</tt>
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to an Exabyte tape drive connected to a Sun called komodo, use:
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<tt>/usr/bin/tar cf komodo:/dev/nrst8 . 2>&1</tt>.
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For versions without remote device support, you can use a pipeline
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and <tt>rsh(1)</tt> to send the
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data to a remote tape drive. (XXX add an example command)
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<sect1><heading> Cpio</heading>
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<!--gen-->
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<p><tt>cpio(1)</tt> is the original Unix file interchange
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tape program for magnetic media. <tt>cpio(1)</tt> has options (among
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many others) to perform byte-swapping, write a number of
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different archives format, and pipe the data to other programs.
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This last feature makes <tt>cpio(1)</tt> and excellent choice for
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installation media. <tt>cpio(1)</tt> does not know how to walk
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the directory tree and a list of files must be provided thru <tt>STDIN</tt>.
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<p><tt>cpio(1)</tt> does not support backups across the
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network. You can use a pipeline and <tt>rsh(1)</tt> to send the
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data to a remote tape drive. (XXX add an example command)
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<sect1><heading> Pax</heading>
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<!--gen-->
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<p><tt>pax(1)</tt> is IEEE/POSIX's answer to <tt>tar</tt> and
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<tt>cpio</tt>. Over the years the various versions of <tt>tar</tt> and
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<tt>cpio</tt> have gotten slightly incompatible. So rather than fight it
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out to fully standardize them, POSIX created a new archive utility.
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<tt>pax</tt> attempts to read and write many of the various cpio and tar
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formats, plus new formats of its own. Its command set more resembles
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<tt>cpio</tt> than <tt>tar</tt>.
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<sect1><heading> Amanda<label id="backups:programs:amanda"></heading>
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<p><htmlurl url="http://www.freebsd.org/ports/misc.html#amanda-2.4.0"
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name="Amanda"> (Advanced Maryland Network Disk Archiver) is a
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client/server backup system, rather than a single program. An
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Amanda server will backup to a single tape drive any number of
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computers that have Amanda clients and network communications
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with the Amanda server. A common problem at locations with a
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number of large disks is the length of time required to backup to
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data directly to tape exceeds the amount of time available for
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the task. Amanda solves this problem. Amanda can use a "holding
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disk" to backup several filesystems at the same time. Amanda
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creates "archive sets": a group of tapes used over a period of
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time to create full backups of all the filesystems listed in
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Amanda's configuration file. The "archive set" also contains
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nightly incremental (or differential) backups of all the
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filesystems. Restoring a damaged filesystem requires the most
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recent full backup and the incremental backups.
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<p>The configuration file provides fine control backups
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and the network traffic that Amanda generates. Amanda will use
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any of the above backup programs to write the data to tape.
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Amanda is available as either a port or a package, it is not
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installed by default.
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<sect1><heading> Do nothing</heading>
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<p>"Do nothing" is not a computer program, but it is the
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most widely used backup strategy. There are no initial costs.
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There is no backup schedule to follow. Just say no. If
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something happens to your data, grin and bear it!
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<p>If your time and your data is worth little to nothing,
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then "Do nothing" is the most suitable backup program for your
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computer. But beware, Unix is a useful tool, you may find that
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within six months you have a collection of files that are
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valuable to you.
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<p>"Do nothing" is the correct backup method for
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<tt>/usr/obj</tt> and other directory trees that can be exactly
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recreated by your computer. An example is the files that
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comprise these handbook pages-they have been generated from
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<tt>SGML</tt> input files. Creating backups of these
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<tt>HTML</tt> files is not necessary. The <tt>SGML</tt> source
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files are backed up regularly.
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<sect1><heading> Which Backup Program is Best?</heading>
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<p><tt>dump(8)</tt> <em>Period.</em> Elizabeth D. Zwicky
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torture tested all the backup programs discussed here. The clear
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choice for preserving all your data and all the peculiarities of
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Unix filesystems is <tt>dump(8)</tt>. Elizabeth created
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filesystems containing a large variety of unusual conditions (and
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some not so unusual ones) and tested each program by do a backup
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and restore of that filesystems. The peculiarities included:
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files with holes, files with holes and a block of nulls, files
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with funny characters in their names, unreadable and unwritable
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files, devices, files that change size during the backup, files
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that are created/deleted during the backup and more. She
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presented the results at LISA V in Oct. 1991.
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<sect1><heading>Emergency Restore Procedure</heading>
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<sect2><heading> Before the Disaster</heading>
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<p>There are only four steps that you need to perform in
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preparation for any disaster that may occur.
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<p>First, print the disklabel from each of your disks
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(<tt>e.g. disklabel sd0 | lpr</tt>), your filesystem table
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(<tt>/etc/fstab</tt>) and all boot messages, two copies of each.
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<p>Second, determine the boot and fixit floppies
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(boot.flp and fixit.flp) have all your devices. The easiest way
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to check is to reboot your machine with the boot floppy in the
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floppy drive and check the boot messages. If all your devices
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are listed and functional, skip on to step three.
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<p>Otherwise, you have to create two custom bootable
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floppies which has a kernel that can mount your all of your disks
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and access your tape drive. These floppies must contain:
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<tt>fdisk(8)</tt>, <tt>disklabel(8)</tt>, <tt>newfs(8)</tt>,
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<tt>mount(8)</tt>, and whichever backup program you use. These
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programs must be statically linked. If you use <tt>dump(8)</tt>,
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the floppy must contain <tt>restore(8)</tt>.
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<p>Third, create backup tapes regularly.
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Any changes that you make after your last backup may be
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irretrievably lost. Write-protect the backup tapes.
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<p>Fourth, test the floppies (either boot.flp and
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fixit.flp or the two custom bootable floppies you made in step
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two.) and backup tapes. Make notes of the procedure. Store
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these notes with the bootable floppy, the printouts and the
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backup tapes. You will be so distraught when restoring that the
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notes may prevent you from destroying your backup tapes (How? In
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place of <tt>tar xvf /dev/rst0</tt>, you might accidently type
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<tt> tar cvf /dev/rst0</tt> and over-write your backup tape).
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<p>For an added measure of security, make bootable
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floppies and two backup tapes each time. Store one of each at a
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remote location. A remote location is NOT the basement of the
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same office building. A number of firms in the World Trade Center
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learned this lesson the hard way. A remote location should be
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physically separated from your computers and disk drives by a
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significant distance.
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<p>An example script for creating a bootable floppy:
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<tscreen><verb>
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#!/bin/sh
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#
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# create a restore floppy
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#
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# format the floppy
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#
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PATH=/bin:/sbin:/usr/sbin:/usr/bin
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fdformat -q fd0
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if [ $? -ne 0 ]
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then
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echo "Bad floppy, please use a new one"
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exit 1
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fi
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# place boot blocks on the floppy
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#
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disklabel -w -B -b /usr/mdec/fdboot -s /usr/mdec/bootfd /dev/rfd0c fd1440
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#
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# newfs the one and only partition
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#
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newfs -t 2 -u 18 -l 1 -c 40 -i 5120 -m 5 -o space /dev/rfd0a
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#
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# mount the new floppy
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#
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mount /dev/fd0a /mnt
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#
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# create required directories
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#
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mkdir /mnt/dev
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mkdir /mnt/bin
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mkdir /mnt/sbin
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mkdir /mnt/etc
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mkdir /mnt/root
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mkdir /mnt/mnt # for the root partition
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mkdir /mnt/tmp
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mkdir /mnt/var
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#
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# populate the directories
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#
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if [ ! -x /sys/compile/MINI/kernel ]
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then
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cat << EOM
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The MINI kernel does not exist, please create one.
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Here is an example config file:
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#
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# MINI -- A kernel to get FreeBSD on onto a disk.
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#
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machine "i386"
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cpu "I486_CPU"
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ident MINI
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maxusers 5
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options INET # needed for _tcp _icmpstat _ipstat
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# _udpstat _tcpstat _udb
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options FFS #Berkeley Fast File System
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options FAT_CURSOR #block cursor in syscons or pccons
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options SCSI_DELAY=15 #Be pessimistic about Joe SCSI device
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options NCONS=2 #1 virtual consoles
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options USERCONFIG #Allow user configuration with -c XXX
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config kernel root on sd0 swap on sd0 and sd1 dumps on sd0
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controller isa0
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controller pci0
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controller fdc0 at isa? port "IO_FD1" bio irq 6 drq 2 vector fdintr
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disk fd0 at fdc0 drive 0
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controller ncr0
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controller scbus0
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device sc0 at isa? port "IO_KBD" tty irq 1 vector scintr
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device npx0 at isa? port "IO_NPX" irq 13 vector npxintr
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device sd0
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device sd1
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device sd2
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device st0
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pseudo-device loop # required by INET
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pseudo-device gzip # Exec gzipped a.out's
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EOM
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exit 1
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fi
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cp -f /sys/compile/MINI/kernel /mnt
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gzip -c -best /sbin/init > /mnt/sbin/init
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gzip -c -best /sbin/fsck > /mnt/sbin/fsck
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gzip -c -best /sbin/mount > /mnt/sbin/mount
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gzip -c -best /sbin/halt > /mnt/sbin/halt
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gzip -c -best /sbin/restore > /mnt/sbin/restore
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gzip -c -best /bin/sh > /mnt/bin/sh
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gzip -c -best /bin/sync > /mnt/bin/sync
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cp /root/.profile /mnt/root
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cp -f /dev/MAKEDEV /mnt/dev
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chmod 755 /mnt/dev/MAKEDEV
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chmod 500 /mnt/sbin/init
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|
chmod 555 /mnt/sbin/fsck /mnt/sbin/mount /mnt/sbin/halt
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chmod 555 /mnt/bin/sh /mnt/bin/sync
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chmod 6555 /mnt/sbin/restore
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|
#
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|
# create the devices nodes
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#
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|
cd /mnt/dev
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./MAKEDEV std
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|
./MAKEDEV sd0
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|
./MAKEDEV sd1
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./MAKEDEV sd2
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|
./MAKEDEV st0
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|
./MAKEDEV pty0
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|
cd /
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|
|
#
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|
# create minimum filesystem table
|
|
#
|
|
cat > /mnt/etc/fstab <<EOM
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|
/dev/fd0a / ufs rw 1 1
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EOM
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|
|
|
#
|
|
# create minimum passwd file
|
|
#
|
|
cat > /mnt/etc/passwd <<EOM
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|
root:*:0:0:Charlie &:/root:/bin/sh
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|
EOM
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|
|
|
cat > /mnt/etc/master.passwd <<EOM
|
|
root::0:0::0:0:Charlie &:/root:/bin/sh
|
|
EOM
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|
|
|
chmod 600 /mnt/etc/master.passwd
|
|
chmod 644 /mnt/etc/passwd
|
|
/usr/sbin/pwd_mkdb -d/mnt/etc /mnt/etc/master.passwd
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|
|
|
#
|
|
# umount the floppy and inform the user
|
|
#
|
|
/sbin/umount /mnt
|
|
</verb></tscreen>
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|
|
<sect2><heading>After the Disaster</heading>
|
|
<p>The key question is: did your hardware survive? You
|
|
have been doing regular backups so there is no need to worry
|
|
about the software.
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|
|
|
<p>If the hardware has been damaged. First, replace
|
|
those parts that have been damaged.
|
|
|
|
<p>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.
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|
|
|
<p>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. <tt>restore</tt> and
|
|
the other programs that you need are located in <tt>/mnt2/stand</tt>.
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|
|
|
<p>Recover each filesystem separately.
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|
|
|
<p>Try to <tt>mount(8) (e.g. mount /dev/sd0a /mnt) </tt>
|
|
the root partition of your first disk. If the disklabel was
|
|
damaged, use <tt>disklabel(8)</tt> to re-partition and label the
|
|
disk to match the label that your printed and saved. Use
|
|
<tt>newfs(8)</tt> to re-create the filesystems. Re-mount the
|
|
root partition of the floppy read-write ("<tt>mount -u -o rw
|
|
/mnt</tt>"). Use your backup program and backup tapes to recover
|
|
the data for this filesystem (e.g. <tt>restore vrf
|
|
/dev/st0</tt>). Unmount the filesystem (e.g. <tt>umount
|
|
/mnt</tt>) Repeat for each filesystem that was damaged.
|
|
|
|
<p>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.
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|
|
|
<sect2><heading>* I did not prepare for the Disaster, What Now?</heading>
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|