731 lines
28 KiB
Text
731 lines
28 KiB
Text
<!--
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The FreeBSD Documentation Project
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$FreeBSD: doc/en_US.ISO_8859-1/books/handbook/backups/chapter.sgml,v 1.28 2001/04/09 00:33:48 dd Exp $
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-->
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<chapter id="backups">
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<title>Backups</title>
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<sect1>
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<title>Synopsis</title>
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<para>The following chapter will cover methods of backing up data, and
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the programs used to create those backups. If you would like to
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contribute something to this section, send it to the &a.doc;.</para>
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</sect1>
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<sect1 id="backups-tapebackups">
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<title>Tape Media</title>
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<para>The major tape media are the 4mm, 8mm, QIC, mini-cartridge and
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DLT.</para>
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<sect2 id="backups-tapebackups-4mm">
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<title>4mm (DDS: Digital Data Storage)</title>
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<para>4mm tapes are replacing QIC as the workstation backup media of
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choice. This trend accelerated greatly when Conner purchased Archive,
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a leading manufacturer of QIC drives, and then stopped production of
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QIC drives. 4mm drives are small and quiet but do not have the
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reputation for reliability that is enjoyed by 8mm drives. The
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cartridges are less expensive and smaller (3 x 2 x 0.5 inches, 76 x 51
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x 12 mm) than 8mm cartridges. 4mm, like 8mm, has comparatively short
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head life for the same reason, both use helical scan.</para>
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<para>Data throughput on these drives starts ~150kB/s, peaking at ~500kB/s.
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Data capacity starts at 1.3 GB and ends at 2.0 GB. Hardware
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compression, available with most of these drives, approximately
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doubles the capacity. Multi-drive tape library units can have 6
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drives in a single cabinet with automatic tape changing. Library
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capacities reach 240 GB.</para>
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<para>The DDS-3 standard now supports tape capacities up to 12GB (or
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24GB compressed).</para>
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<para>4mm drives, like 8mm drives, use helical-scan. All the benefits
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and drawbacks of helical-scan apply to both 4mm and 8mm drives.</para>
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<para>Tapes should be retired from use after 2,000 passes or 100 full
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backups.</para>
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</sect2>
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<sect2 id="backups-tapebackups-8mm">
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<title>8mm (Exabyte)</title>
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<para>8mm tapes are the most common SCSI tape drives; they are the best
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choice of exchanging tapes. Nearly every site has an exabyte 2 GB 8mm
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tape drive. 8mm drives are reliable, convenient and quiet. Cartridges
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are inexpensive and small (4.8 x 3.3 x 0.6 inches; 122 x 84 x 15 mm).
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One downside of 8mm tape is relatively short head and tape life due to
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the high rate of relative motion of the tape across the heads.</para>
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<para>Data throughput ranges from ~250kB/s to ~500kB/s. Data sizes start
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at 300 MB and go up to 7 GB. Hardware compression, available with
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most of these drives, approximately doubles the capacity. These
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drives are available as single units or multi-drive tape libraries
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with 6 drives and 120 tapes in a single cabinet. Tapes are changed
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automatically by the unit. Library capacities reach 840+ GB.</para>
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<para>The Exabyte <quote>Mammoth</quote> model supports 12GB on one tape
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(24GB with compression) and costs approximately twice as much as
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conventional tape drives.</para>
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<para>Data is recorded onto the tape using helical-scan, the heads are
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positioned at an angle to the media (approximately 6 degrees). The
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tape wraps around 270 degrees of the spool that holds the heads. The
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spool spins while the tape slides over the spool. The result is a
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high density of data and closely packed tracks that angle across the
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tape from one edge to the other.</para>
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</sect2>
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<sect2 id="backups-tapebackups-qic">
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<title>QIC</title>
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<para>QIC-150 tapes and drives are, perhaps, the most common tape drive
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and media around. QIC tape drives are the least expensive "serious"
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backup drives. The downside is the cost of media. QIC tapes are
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expensive compared to 8mm or 4mm tapes, up to 5 times the price per GB
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data storage. But, if your needs can be satisfied with a half-dozen
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tapes, QIC may be the correct choice. QIC is the
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<emphasis>most</emphasis> common tape drive. Every site has a QIC
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drive of some density or another. Therein lies the rub, QIC has a
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large number of densities on physically similar (sometimes identical)
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tapes. QIC drives are not quiet. These drives audibly seek before
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they begin to record data and are clearly audible whenever reading,
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writing or seeking. QIC tapes measure (6 x 4 x 0.7 inches; 15.2 x
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10.2 x 1.7 mm). <link
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linkend="backups-tapebackups-mini">Mini-cartridges</link>, which
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also use 1/4" wide tape are discussed separately. Tape libraries and
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changers are not available.</para>
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<para>Data throughput ranges from ~150kB/s to ~500kB/s. Data capacity
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ranges from 40 MB to 15 GB. Hardware compression is available on many
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of the newer QIC drives. QIC drives are less frequently installed;
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they are being supplanted by DAT drives.</para>
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<para>Data is recorded onto the tape in tracks. The tracks run along
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the long axis of the tape media from one end to the other. The number
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of tracks, and therefore the width of a track, varies with the tape's
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capacity. Most if not all newer drives provide backward-compatibility
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at least for reading (but often also for writing). QIC has a good
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reputation regarding the safety of the data (the mechanics are simpler
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and more robust than for helical scan drives).</para>
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<para>Tapes should be retired from use after 5,000 backups.</para>
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</sect2>
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<![ %not.published; [
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<sect2 id="backups-tapebackups-mini">
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<title>* Mini-Cartridge</title>
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<para></para>
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</sect2>
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]]>
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<sect2 id="backups-tapebackups-dlt">
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<title>DLT</title>
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<para>DLT has the fastest data transfer rate of all the drive types
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listed here. The 1/2" (12.5mm) tape is contained in a single spool
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cartridge (4 x 4 x 1 inches; 100 x 100 x 25 mm). The cartridge has a
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swinging gate along one entire side of the cartridge. The drive
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mechanism opens this gate to extract the tape leader. The tape leader
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has an oval hole in it which the drive uses to "hook" the tape. The
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take-up spool is located inside the tape drive. All the other tape
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cartridges listed here (9 track tapes are the only exception) have
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both the supply and take-up spools located inside the tape cartridge
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itself.</para>
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<para>Data throughput is approximately 1.5MB/s, three times the throughput of
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4mm, 8mm, or QIC tape drives. Data capacities range from 10GB to 20GB
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for a single drive. Drives are available in both multi-tape changers
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and multi-tape, multi-drive tape libraries containing from 5 to 900
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tapes over 1 to 20 drives, providing from 50GB to 9TB of
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storage.</para>
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<para>With compression, DLT Type IV format supports up to 70GB
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capacity.</para>
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<para>Data is recorded onto the tape in tracks parallel to the direction
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of travel (just like QIC tapes). Two tracks are written at once.
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Read/write head lifetimes are relatively long; once the tape stops
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moving, there is no relative motion between the heads and the
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tape.</para>
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</sect2>
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<sect2>
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<title id="backups-tapebackups-ait">AIT</title>
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<para>AIT is a new format from Sony, and can hold up to 50GB (with
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compression) per tape. The tapes contain memory chips which retain an
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index of the tape's contents. This index can be rapidly read by the
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tape drive to determine the position of files on the tape, instead of
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the several minutes that would be required for other tapes. Software
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such as SAMS:Alexandria can operate forty or more AIT tape libraries,
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communicating directly with the tape's memory chip to display the
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contents on screen, determine what files where backed up to which
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tape, locate the correct tape, load it, and restore the data from the
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tape.</para>
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<para>Libraries like this cost in the region of $20,000, pricing them a
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little out of the hobbyist market.</para>
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</sect2>
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<sect2>
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<title>Using a New Tape for the First Time</title>
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<para>The first time that you try to read or write a new, completely
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blank tape, the operation will fail. The console messages should be
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similar to:</para>
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<screen>sa0(ncr1:4:0): NOT READY asc:4,1
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sa0(ncr1:4:0): Logical unit is in process of becoming ready</screen>
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<para>The tape does not contain an Identifier Block (block number 0).
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All QIC tape drives since the adoption of QIC-525 standard write an
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Identifier Block to the tape. There are two solutions:</para>
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<para><command>mt fsf 1</command> causes the tape drive to write an
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Identifier Block to the tape.</para>
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<para>Use the front panel button to eject the tape.</para>
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<para>Re-insert the tape and &man.dump.8; data to the tape.</para>
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<para>&man.dump.8; will report <literal>DUMP: End of tape
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detected</literal> and the console will show: <literal>HARDWARE
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FAILURE info:280 asc:80,96</literal></para>
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<para>rewind the tape using: <command>mt rewind</command></para>
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<para>Subsequent tape operations are successful.</para>
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</sect2>
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</sect1>
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<sect1 id="backup-programs">
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<title>Backup Programs</title>
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<para>The three major programs are
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&man.dump.8;,
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&man.tar.1;,
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and
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&man.cpio.1;.</para>
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<sect2>
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<title>Dump and Restore</title>
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<para>&man.dump.8; and &man.restore.8; are the traditional Unix backup
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programs. They operate on the drive as a collection of disk blocks,
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below the abstractions of files, links and directories that are
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created by the filesystems. &man.dump.8; backs up devices, entire
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filesystems, not parts of a filesystem and not directory trees that
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span more than one filesystem, using either soft links &man.ln.1; or
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mounting one filesystem onto another. &man.dump.8; does not write
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files and directories to tape, but rather writes the data blocks that
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are the building blocks of files and directories. &man.dump.8; has
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quirks that remain from its early days in Version 6 of ATT Unix (circa
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1975). The default parameters are suitable for 9-track tapes (6250
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bpi), not the high-density media available today (up to 62,182 ftpi).
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These defaults must be overridden on the command line to utilize the
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capacity of current tape drives.</para>
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<para>&man.rdump.8; and &man.rrestore.8; backup data across the network
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to a tape drive attached to another computer. Both programs rely upon
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&man.rcmd.3; and &man.ruserok.3; to access the remote tape drive.
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Therefore, the user performing the backup must have
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<literal>rhosts</literal> access to the remote computer. The
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arguments to &man.rdump.8; and &man.rrestore.8; must suitable to use
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on the remote computer. (e.g. When <command>rdump</command>ing from
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a FreeBSD computer to an Exabyte tape drive connected to a Sun called
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<hostid>komodo</hostid>, use: <command>/sbin/rdump 0dsbfu 54000 13000
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126 komodo:/dev/nrsa8 /dev/rda0a 2>&1</command>) Beware: there
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are security implications to allowing <literal>rhosts</literal>
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commands. Evaluate your situation carefully.</para>
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</sect2>
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<sect2>
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<title>Tar</title>
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<para>&man.tar.1; also dates back to Version 6 of ATT Unix (circa 1975).
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&man.tar.1; operates in cooperation with the filesystem; &man.tar.1;
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writes files and directories to tape. &man.tar.1; does not support the
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full range of options that are available from &man.cpio.1;, but
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&man.tar.1; does not require the unusual command pipeline that
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&man.cpio.1; uses.</para>
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<para>Most versions of &man.tar.1; do not support backups across the
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network. The GNU version of &man.tar.1;, which FreeBSD utilizes,
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supports remote devices using the same syntax as &man.rdump.8;. To
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&man.tar.1; to an Exabyte tape drive connected to a Sun called
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<hostid>komodo</hostid>, use: <command>/usr/bin/tar cf
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komodo:/dev/nrsa8 . 2>&1</command>. For versions without remote
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device support, you can use a pipeline and &man.rsh.1; to send the
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data to a remote tape drive.</para>
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<screen>&prompt.root; <userinput>tar cf - . | rsh <replaceable>hostname</replaceable> dd of=<replaceable>tape-device</replaceable> obs=20b</userinput></screen>
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<para>If you're worried about the security of backing over a network
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you should use the &man.ssh.1; command instead of &man.rsh.1;.</para>
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</sect2>
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<sect2>
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<title>Cpio</title>
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<para>&man.cpio.1; is the original Unix file interchange tape program
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for magnetic media. &man.cpio.1; has options (among many others) to
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perform byte-swapping, write a number of different archives format,
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and pipe the data to other programs. This last feature makes
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&man.cpio.1; and excellent choice for installation media.
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&man.cpio.1; does not know how to walk the directory tree and a list
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of files must be provided through <filename>stdin</filename>.</para>
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<para>&man.cpio.1; does not support backups across the network. You can
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use a pipeline and &man.rsh.1; to send the data to a remote tape
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drive. (XXX add an example command)</para>
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</sect2>
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<sect2>
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<title>Pax</title>
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<para>&man.pax.1; is IEEE/POSIX's answer to &man.tar.1; and
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&man.cpio.1;. Over the years the various versions of &man.tar.1;
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and &man.cpio.1; have gotten slightly incompatible. So rather than
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fight it out to fully standardize them, POSIX created a new archive
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utility. &man.pax.1; attempts to read and write many of the various
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&man.cpio.1; and &man.tar.1; formats, plus new formats of its own.
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Its command set more resembles &man.cpio.1; than &man.tar.1;.</para>
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</sect2>
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<sect2 id="backups-programs-amanda">
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<title>Amanda</title>
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<para><ulink url="../ports/misc.html#amanda-2.4.0">Amanda</ulink>
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(Advanced Maryland Network Disk Archiver) is a client/server backup
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system, rather than a single program. An Amanda server will backup to
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a single tape drive any number of computers that have Amanda clients
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and network communications with the Amanda server. A common problem
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at locations with a number of large disks is the length of time
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required to backup to data directly to tape exceeds the amount of time
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available for the task. Amanda solves this problem. Amanda can use a
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"holding 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 time to
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create full backups of all the filesystems listed in Amanda's
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configuration file. The "archive set" also contains nightly
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incremental (or differential) backups of all the filesystems.
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Restoring a damaged filesystem requires the most recent full backup
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and the incremental backups.</para>
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<para>The configuration file provides fine control backups and the
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network traffic that Amanda generates. Amanda will use any of the
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above backup programs to write the data to tape. Amanda is available
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as either a port or a package, it is not installed by default.</para>
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</sect2>
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<sect2>
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<title>Do Nothing</title>
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<para><quote>Do nothing</quote> is not a computer program, but it is the
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most widely used backup strategy. There are no initial costs. There
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is no backup schedule to follow. Just say no. If something happens
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to your data, grin and bear it!</para>
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<para>If your time and your data is worth little to nothing, then
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<quote>Do nothing</quote> is the most suitable backup program for your
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computer. But beware, Unix is a useful tool, you may find that within
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six months you have a collection of files that are valuable to
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you.</para>
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<para><quote>Do nothing</quote> is the correct backup method for
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<filename>/usr/obj</filename> and other directory trees that can be
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exactly 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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<acronym>SGML</acronym> input files. Creating backups of these
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<acronym>HTML</acronym> files is not necessary. The
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<acronym>SGML</acronym> source files are backed up regularly.</para>
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</sect2>
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<sect2>
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<title>Which Backup Program is Best?</title>
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<para>&man.dump.8; <emphasis>Period.</emphasis> 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 Unix
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filesystems is &man.dump.8;. Elizabeth created filesystems containing
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a large variety of unusual conditions (and some not so unusual ones)
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and tested each program by doing a backup and restore of that
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filesystems. The peculiarities included: files with holes, files with
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holes and a block of nulls, files with funny characters in their
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names, unreadable and unwritable files, devices, files that change
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size during the backup, files that are created/deleted during the
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backup and more. She presented the results at LISA V in Oct. 1991.
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See <ulink
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url="http://reality.sgi.com/zwicky_neu/testdump.doc.html">torture-testing
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Backup and Archive Programs</ulink>.</para>
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</sect2>
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<sect2>
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<title>Emergency Restore Procedure</title>
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<sect3>
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<title>Before the Disaster</title>
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<para>There are only four steps that you need to perform in
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preparation for any disaster that may occur.</para>
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<para>First, print the disklabel from each of your disks
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(<command>e.g. disklabel da0 | lpr</command>), your filesystem table
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(<filename>/etc/fstab</filename>) and all boot messages,
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two copies of
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each.</para>
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<para>Second, determine that the boot and fix-it floppies
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(<filename>boot.flp</filename> and <filename>fixit.flp</filename>)
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have all your devices. The easiest way to check is to reboot your
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machine with the boot floppy in the floppy drive and check the boot
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messages. If all your devices are listed and functional, skip on to
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step three.</para>
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<para>Otherwise, you have to create two custom bootable floppies which
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has a kernel that can mount your all of your disks and access your
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tape drive. These floppies must contain:
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&man.fdisk.8;, &man.disklabel.8;, &man.newfs.8;, &man.mount.8;, and
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whichever backup program you use. These programs must be statically
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linked. If you use &man.dump.8;, the floppy must contain
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&man.restore.8;.</para>
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<para>Third, create backup tapes regularly. Any changes that you make
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after your last backup may be irretrievably lost. Write-protect the
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backup tapes.</para>
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<para>Fourth, test the floppies (either <filename>boot.flp</filename>
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and <filename>fixit.flp</filename> or the two custom bootable
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floppies you made in step two.) and backup tapes. Make notes of the
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procedure. Store these notes with the bootable floppy, the
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printouts and the backup tapes. You will be so distraught when
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restoring that the notes may prevent you from destroying your backup
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tapes (How? In place of <command>tar xvf /dev/rsa0</command>, you
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might accidently type <command>tar cvf /dev/rsa0</command> and
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over-write your backup tape).</para>
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<para>For an added measure of security, make bootable floppies and two
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backup tapes each time. Store one of each at a remote location. A
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remote location is NOT the basement of the same office building. A
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number of firms in the World Trade Center learned this lesson the
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hard way. A remote location should be physically separated from
|
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your computers and disk drives by a significant distance.</para>
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<para>An example script for creating a bootable floppy:</para>
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<programlisting><![ CDATA [#!/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
|
|
if [ $? -ne 0 ]
|
|
then
|
|
echo "Bad floppy, please use a new one"
|
|
exit 1
|
|
fi
|
|
|
|
# place boot blocks on the floppy
|
|
#
|
|
disklabel -w -B /dev/fd0c fd1440
|
|
|
|
#
|
|
# newfs the one and only partition
|
|
#
|
|
newfs -t 2 -u 18 -l 1 -c 40 -i 5120 -m 5 -o space /dev/fd0a
|
|
|
|
#
|
|
# mount the new floppy
|
|
#
|
|
mount /dev/fd0a /mnt
|
|
|
|
#
|
|
# create required directories
|
|
#
|
|
mkdir /mnt/dev
|
|
mkdir /mnt/bin
|
|
mkdir /mnt/sbin
|
|
mkdir /mnt/etc
|
|
mkdir /mnt/root
|
|
mkdir /mnt/mnt # for the root partition
|
|
mkdir /mnt/tmp
|
|
mkdir /mnt/var
|
|
|
|
#
|
|
# populate the directories
|
|
#
|
|
if [ ! -x /sys/compile/MINI/kernel ]
|
|
then
|
|
cat << EOM
|
|
The MINI kernel does not exist, please create one.
|
|
Here is an example config file:
|
|
#
|
|
# MINI -- A kernel to get FreeBSD on onto a disk.
|
|
#
|
|
machine "i386"
|
|
cpu "I486_CPU"
|
|
ident MINI
|
|
maxusers 5
|
|
|
|
options INET # needed for _tcp _icmpstat _ipstat
|
|
# _udpstat _tcpstat _udb
|
|
options FFS #Berkeley Fast File System
|
|
options FAT_CURSOR #block cursor in syscons or pccons
|
|
options SCSI_DELAY=15 #Be pessimistic about Joe SCSI device
|
|
options NCONS=2 #1 virtual consoles
|
|
options USERCONFIG #Allow user configuration with -c XXX
|
|
|
|
config kernel root on da0 swap on da0 and da1 dumps on da0
|
|
|
|
controller isa0
|
|
controller pci0
|
|
|
|
controller fdc0 at isa? port "IO_FD1" bio irq 6 drq 2 vector fdintr
|
|
disk fd0 at fdc0 drive 0
|
|
|
|
controller ncr0
|
|
|
|
controller scbus0
|
|
|
|
device sc0 at isa? port "IO_KBD" tty irq 1 vector scintr
|
|
device npx0 at isa? port "IO_NPX" irq 13 vector npxintr
|
|
|
|
device da0
|
|
device da1
|
|
device da2
|
|
|
|
device sa0
|
|
|
|
pseudo-device loop # required by INET
|
|
pseudo-device gzip # Exec gzipped a.out's
|
|
EOM
|
|
exit 1
|
|
fi
|
|
|
|
cp -f /sys/compile/MINI/kernel /mnt
|
|
|
|
gzip -c -best /sbin/init > /mnt/sbin/init
|
|
gzip -c -best /sbin/fsck > /mnt/sbin/fsck
|
|
gzip -c -best /sbin/mount > /mnt/sbin/mount
|
|
gzip -c -best /sbin/halt > /mnt/sbin/halt
|
|
gzip -c -best /sbin/restore > /mnt/sbin/restore
|
|
|
|
gzip -c -best /bin/sh > /mnt/bin/sh
|
|
gzip -c -best /bin/sync > /mnt/bin/sync
|
|
|
|
cp /root/.profile /mnt/root
|
|
|
|
cp -f /dev/MAKEDEV /mnt/dev
|
|
chmod 755 /mnt/dev/MAKEDEV
|
|
|
|
chmod 500 /mnt/sbin/init
|
|
chmod 555 /mnt/sbin/fsck /mnt/sbin/mount /mnt/sbin/halt
|
|
chmod 555 /mnt/bin/sh /mnt/bin/sync
|
|
chmod 6555 /mnt/sbin/restore
|
|
|
|
#
|
|
# create the devices nodes
|
|
#
|
|
cd /mnt/dev
|
|
./MAKEDEV std
|
|
./MAKEDEV da0
|
|
./MAKEDEV da1
|
|
./MAKEDEV da2
|
|
./MAKEDEV sa0
|
|
./MAKEDEV pty0
|
|
cd /
|
|
|
|
#
|
|
# create minimum filesystem table
|
|
#
|
|
cat > /mnt/etc/fstab <<EOM
|
|
/dev/fd0a / ufs rw 1 1
|
|
EOM
|
|
|
|
#
|
|
# create minimum passwd file
|
|
#
|
|
cat > /mnt/etc/passwd <<EOM
|
|
root:*:0:0:Charlie &:/root:/bin/sh
|
|
EOM
|
|
|
|
cat > /mnt/etc/master.passwd <<EOM
|
|
root::0:0::0:0:Charlie &:/root:/bin/sh
|
|
EOM
|
|
|
|
chmod 600 /mnt/etc/master.passwd
|
|
chmod 644 /mnt/etc/passwd
|
|
/usr/sbin/pwd_mkdb -d/mnt/etc /mnt/etc/master.passwd
|
|
|
|
#
|
|
# umount the floppy and inform the user
|
|
#
|
|
/sbin/umount /mnt
|
|
echo "The floppy has been unmounted and is now ready."]]></programlisting>
|
|
</sect3>
|
|
|
|
<sect3>
|
|
<title>After the Disaster</title>
|
|
|
|
<para>The key question is: did your hardware survive? You have been
|
|
doing regular backups so there is no need to worry about the
|
|
software.</para>
|
|
|
|
<para>If the hardware has been damaged. First, replace those parts
|
|
that have been damaged.</para>
|
|
|
|
<para>If your hardware is okay, check your floppies. If you are using
|
|
a custom boot floppy, boot single-user (type <literal>-s</literal>
|
|
at the <prompt>boot:</prompt> prompt). Skip the following
|
|
paragraph.</para>
|
|
|
|
<para>If you are using the <filename>boot.flp</filename> and
|
|
<filename>fixit.flp</filename> floppies, keep reading. Insert the
|
|
<filename>boot.flp</filename> floppy in the first floppy drive and
|
|
boot the computer. The original install menu will be displayed on
|
|
the screen. Select the <literal>Fixit--Repair mode with CDROM or
|
|
floppy.</literal> option. Insert the
|
|
<filename>fixit.flp</filename> when prompted.
|
|
<command>restore</command> and the other programs that you need are
|
|
located in <filename>/mnt2/stand</filename>.</para>
|
|
|
|
<para>Recover each filesystem separately.</para>
|
|
|
|
<para>Try to &man.mount.8; (e.g. <command>mount /dev/da0a
|
|
/mnt</command>) 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 (<command>mount -u -o rw
|
|
/mnt</command>). Use your backup program and backup tapes to
|
|
recover the data for this filesystem (e.g. <command>restore vrf
|
|
/dev/sa0</command>). Unmount the filesystem (e.g. <command>umount
|
|
/mnt</command>) Repeat for each filesystem that was
|
|
damaged.</para>
|
|
|
|
<para>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.</para>
|
|
</sect3>
|
|
|
|
<![ %not.published; [
|
|
|
|
<sect3>
|
|
<title>* I did not prepare for the Disaster, What Now?</title>
|
|
|
|
<para></para>
|
|
</sect3>
|
|
]]>
|
|
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1 id="backups-floppybackups">
|
|
<title>What about Backups to Floppies?</title>
|
|
|
|
<sect2 id="floppies-using">
|
|
<title>Can I use floppies for backing up my data?</title>
|
|
|
|
<para>Floppy disks are not really a suitable media for
|
|
making backups as:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>The media is unreliable, especially over long periods of
|
|
time</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Backing up and restoring is very slow</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>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).</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>However, if you have no other method of backing up your data then
|
|
floppy disks are better than no backup at all.</para>
|
|
|
|
<para>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.</para>
|
|
</sect2>
|
|
|
|
<sect2 id="floppies-creating">
|
|
<title>So how do I backup my data to floppies?</title>
|
|
|
|
<para>The best way to backup to floppy disk is to use
|
|
&man.tar.1; with the <option>-M</option> (multi volume) option, which
|
|
allows backups to span multiple floppies.</para>
|
|
|
|
<para>To backup all the files in the current directory and sub-directory
|
|
use this (as root):</para>
|
|
|
|
<screen>&prompt.root; <userinput>tar Mcvf /dev/fd0 *</userinput></screen>
|
|
|
|
<para>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)</para>
|
|
|
|
<screen>Prepare volume #2 for /dev/fd0 and hit return:</screen>
|
|
|
|
<para>This is repeated (with the volume number incrementing) until all
|
|
the specified files have been archived.</para>
|
|
</sect2>
|
|
|
|
<sect2 id="floppies-compress">
|
|
<title>Can I compress my backups?</title>
|
|
|
|
<para>Unfortunately, &man.tar.1; will not allow the
|
|
<option>-z</option> 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!</para>
|
|
</sect2>
|
|
|
|
<sect2 id="floppies-restoring">
|
|
<title>How do I restore my backups?</title>
|
|
|
|
<para>To restore the entire archive use:</para>
|
|
|
|
<screen>&prompt.root; <userinput>tar Mxvf /dev/fd0</userinput></screen>
|
|
|
|
<para>To restore only specific files you can either start with the first
|
|
floppy and use:</para>
|
|
|
|
<screen>&prompt.root; <userinput>tar Mxvf /dev/fd0 <replaceable>filename</replaceable></userinput></screen>
|
|
|
|
<para>&man.tar.1; will prompt you to insert subsequent floppies until it
|
|
finds the required file.</para>
|
|
|
|
<para>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!</para>
|
|
</sect2>
|
|
</sect1>
|
|
</chapter>
|
|
|
|
<!--
|
|
Local Variables:
|
|
mode: sgml
|
|
sgml-declaration: "../chapter.decl"
|
|
sgml-indent-data: t
|
|
sgml-omittag: nil
|
|
sgml-always-quote-attributes: t
|
|
sgml-parent-document: ("../book.sgml" "part" "chapter")
|
|
End:
|
|
-->
|