Rework the Storage chapter a bit. Move information on tapes to the lower
part of the chapter. PR: 41244
This commit is contained in:
Tom Rhodes
parent
9eaa38b590
commit
46168b00b3
Notes:
svn2git
2020-12-08 03:00:23 +00:00
svn path=/head/; revision=14025
1 changed files with 214 additions and 214 deletions
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@ -1429,223 +1429,12 @@ sh MAKEDEV ccd0</programlisting>
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</para>
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</sect2>
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</sect1>
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<sect1 id="backups-tapebackups">
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<title>Tape Backup Media</title>
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<indexterm><primary>tape media</primary></indexterm>
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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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<indexterm>
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<primary>tape media</primary>
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<secondary>DDS (4mm) tapes</secondary>
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</indexterm>
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<indexterm>
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<primary>tape media</primary>
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<secondary>QIC tapes</secondary>
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</indexterm>
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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 12 GB (or
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24 GB 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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<indexterm>
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<primary>tape media</primary>
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<secondary>Exabyte (8mm) tapes</secondary>
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</indexterm>
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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 12 GB on one tape
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(24 GB 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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<indexterm>
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<primary>tape media</primary>
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<secondary>QIC-150</secondary>
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</indexterm>
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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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<sect2 id="backups-tapebackups-mini">
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<title>XXX* Mini-Cartridge</title>
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<para></para>
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</sect2>
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<sect2 id="backups-tapebackups-dlt">
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<title>DLT</title>
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<indexterm>
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<primary>tape media</primary>
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<secondary>DLT</secondary>
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</indexterm>
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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 10 GB to 20 GB
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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 50 GB to 9 TB of
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storage.</para>
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<para>With compression, DLT Type IV format supports up to 70 GB
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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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<indexterm>
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<primary>tape media</primary>
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<secondary>AIT</secondary>
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</indexterm>
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<para>AIT is a new format from Sony, and can hold up to 50 GB (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 were 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 <command>dump</command> data to the tape.</para>
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<para><command>dump</command> 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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<sect1 id="backup-basics">
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<title>Backup Programs</title>
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<indexterm><primary>backup software</primary></indexterm>
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<indexterm><primary>backup software and basics</primary></indexterm>
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<para>The three major programs are
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<para>The three major backup 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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@ -2411,6 +2200,217 @@ echo "The floppy has been unmounted and is now ready."]]></programlisting>
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restore it, even if you have not asked it to!</para>
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</sect2>
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</sect1>
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<sect1 id="backups-tapebackups">
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<title>Tape Backup Media</title>
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<indexterm><primary>tape media</primary></indexterm>
|
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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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|
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<sect2 id="backups-tapebackups-4mm">
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<title>4mm (DDS: Digital Data Storage)</title>
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|
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<indexterm>
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<primary>tape media</primary>
|
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<secondary>DDS (4mm) tapes</secondary>
|
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</indexterm>
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<indexterm>
|
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<primary>tape media</primary>
|
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<secondary>QIC tapes</secondary>
|
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</indexterm>
|
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<para>4mm tapes are replacing QIC as the workstation backup media of
|
||||
choice. This trend accelerated greatly when Conner purchased Archive,
|
||||
a leading manufacturer of QIC drives, and then stopped production of
|
||||
QIC drives. 4mm drives are small and quiet but do not have the
|
||||
reputation for reliability that is enjoyed by 8mm drives. The
|
||||
cartridges are less expensive and smaller (3 x 2 x 0.5 inches, 76 x 51
|
||||
x 12 mm) than 8mm cartridges. 4mm, like 8mm, has comparatively short
|
||||
head life for the same reason, both use helical scan.</para>
|
||||
|
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<para>Data throughput on these drives starts ~150kB/s, peaking at ~500kB/s.
|
||||
Data capacity starts at 1.3 GB and ends at 2.0 GB. Hardware
|
||||
compression, available with most of these drives, approximately
|
||||
doubles the capacity. Multi-drive tape library units can have 6
|
||||
drives in a single cabinet with automatic tape changing. Library
|
||||
capacities reach 240 GB.</para>
|
||||
|
||||
<para>The DDS-3 standard now supports tape capacities up to 12 GB (or
|
||||
24 GB compressed).</para>
|
||||
|
||||
<para>4mm drives, like 8mm drives, use helical-scan. All the benefits
|
||||
and drawbacks of helical-scan apply to both 4mm and 8mm drives.</para>
|
||||
|
||||
<para>Tapes should be retired from use after 2,000 passes or 100 full
|
||||
backups.</para>
|
||||
</sect2>
|
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|
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<sect2 id="backups-tapebackups-8mm">
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<title>8mm (Exabyte)</title>
|
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<indexterm>
|
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<primary>tape media</primary>
|
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<secondary>Exabyte (8mm) tapes</secondary>
|
||||
</indexterm>
|
||||
|
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<para>8mm tapes are the most common SCSI tape drives; they are the best
|
||||
choice of exchanging tapes. Nearly every site has an Exabyte 2 GB 8mm
|
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tape drive. 8mm drives are reliable, convenient and quiet. Cartridges
|
||||
are inexpensive and small (4.8 x 3.3 x 0.6 inches; 122 x 84 x 15 mm).
|
||||
One downside of 8mm tape is relatively short head and tape life due to
|
||||
the high rate of relative motion of the tape across the heads.</para>
|
||||
|
||||
<para>Data throughput ranges from ~250kB/s to ~500kB/s. Data sizes start
|
||||
at 300 MB and go up to 7 GB. Hardware compression, available with
|
||||
most of these drives, approximately doubles the capacity. These
|
||||
drives are available as single units or multi-drive tape libraries
|
||||
with 6 drives and 120 tapes in a single cabinet. Tapes are changed
|
||||
automatically by the unit. Library capacities reach 840+ GB.</para>
|
||||
|
||||
<para>The Exabyte <quote>Mammoth</quote> model supports 12 GB on one tape
|
||||
(24 GB with compression) and costs approximately twice as much as
|
||||
conventional tape drives.</para>
|
||||
|
||||
<para>Data is recorded onto the tape using helical-scan, the heads are
|
||||
positioned at an angle to the media (approximately 6 degrees). The
|
||||
tape wraps around 270 degrees of the spool that holds the heads. The
|
||||
spool spins while the tape slides over the spool. The result is a
|
||||
high density of data and closely packed tracks that angle across the
|
||||
tape from one edge to the other.</para>
|
||||
</sect2>
|
||||
|
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<sect2 id="backups-tapebackups-qic">
|
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<title>QIC</title>
|
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<indexterm>
|
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<primary>tape media</primary>
|
||||
<secondary>QIC-150</secondary>
|
||||
</indexterm>
|
||||
|
||||
<para>QIC-150 tapes and drives are, perhaps, the most common tape drive
|
||||
and media around. QIC tape drives are the least expensive "serious"
|
||||
backup drives. The downside is the cost of media. QIC tapes are
|
||||
expensive compared to 8mm or 4mm tapes, up to 5 times the price per GB
|
||||
data storage. But, if your needs can be satisfied with a half-dozen
|
||||
tapes, QIC may be the correct choice. QIC is the
|
||||
<emphasis>most</emphasis> common tape drive. Every site has a QIC
|
||||
drive of some density or another. Therein lies the rub, QIC has a
|
||||
large number of densities on physically similar (sometimes identical)
|
||||
tapes. QIC drives are not quiet. These drives audibly seek before
|
||||
they begin to record data and are clearly audible whenever reading,
|
||||
writing or seeking. QIC tapes measure (6 x 4 x 0.7 inches; 15.2 x
|
||||
10.2 x 1.7 mm). <link
|
||||
linkend="backups-tapebackups-mini">Mini-cartridges</link>, which
|
||||
also use 1/4" wide tape are discussed separately. Tape libraries and
|
||||
changers are not available.</para>
|
||||
|
||||
<para>Data throughput ranges from ~150kB/s to ~500kB/s. Data capacity
|
||||
ranges from 40 MB to 15 GB. Hardware compression is available on many
|
||||
of the newer QIC drives. QIC drives are less frequently installed;
|
||||
they are being supplanted by DAT drives.</para>
|
||||
|
||||
<para>Data is recorded onto the tape in tracks. The tracks run along
|
||||
the long axis of the tape media from one end to the other. The number
|
||||
of tracks, and therefore the width of a track, varies with the tape's
|
||||
capacity. Most if not all newer drives provide backward-compatibility
|
||||
at least for reading (but often also for writing). QIC has a good
|
||||
reputation regarding the safety of the data (the mechanics are simpler
|
||||
and more robust than for helical scan drives).</para>
|
||||
|
||||
<para>Tapes should be retired from use after 5,000 backups.</para>
|
||||
</sect2>
|
||||
|
||||
<sect2 id="backups-tapebackups-mini">
|
||||
<title>XXX* Mini-Cartridge</title>
|
||||
|
||||
<para></para>
|
||||
</sect2>
|
||||
|
||||
<sect2 id="backups-tapebackups-dlt">
|
||||
<title>DLT</title>
|
||||
<indexterm>
|
||||
<primary>tape media</primary>
|
||||
<secondary>DLT</secondary>
|
||||
</indexterm>
|
||||
|
||||
<para>DLT has the fastest data transfer rate of all the drive types
|
||||
listed here. The 1/2" (12.5mm) tape is contained in a single spool
|
||||
cartridge (4 x 4 x 1 inches; 100 x 100 x 25 mm). The cartridge has a
|
||||
swinging gate along one entire side of the cartridge. The drive
|
||||
mechanism opens this gate to extract the tape leader. The tape leader
|
||||
has an oval hole in it which the drive uses to "hook" the tape. The
|
||||
take-up spool is located inside the tape drive. All the other tape
|
||||
cartridges listed here (9 track tapes are the only exception) have
|
||||
both the supply and take-up spools located inside the tape cartridge
|
||||
itself.</para>
|
||||
|
||||
<para>Data throughput is approximately 1.5MB/s, three times the throughput of
|
||||
4mm, 8mm, or QIC tape drives. Data capacities range from 10 GB to 20 GB
|
||||
for a single drive. Drives are available in both multi-tape changers
|
||||
and multi-tape, multi-drive tape libraries containing from 5 to 900
|
||||
tapes over 1 to 20 drives, providing from 50 GB to 9 TB of
|
||||
storage.</para>
|
||||
|
||||
<para>With compression, DLT Type IV format supports up to 70 GB
|
||||
capacity.</para>
|
||||
|
||||
<para>Data is recorded onto the tape in tracks parallel to the direction
|
||||
of travel (just like QIC tapes). Two tracks are written at once.
|
||||
Read/write head lifetimes are relatively long; once the tape stops
|
||||
moving, there is no relative motion between the heads and the
|
||||
tape.</para>
|
||||
</sect2>
|
||||
|
||||
<sect2>
|
||||
<title id="backups-tapebackups-ait">AIT</title>
|
||||
<indexterm>
|
||||
<primary>tape media</primary>
|
||||
<secondary>AIT</secondary>
|
||||
</indexterm>
|
||||
|
||||
<para>AIT is a new format from Sony, and can hold up to 50 GB (with
|
||||
compression) per tape. The tapes contain memory chips which retain an
|
||||
index of the tape's contents. This index can be rapidly read by the
|
||||
tape drive to determine the position of files on the tape, instead of
|
||||
the several minutes that would be required for other tapes. Software
|
||||
such as SAMS:Alexandria can operate forty or more AIT tape libraries,
|
||||
communicating directly with the tape's memory chip to display the
|
||||
contents on screen, determine what files were backed up to which
|
||||
tape, locate the correct tape, load it, and restore the data from the
|
||||
tape.</para>
|
||||
|
||||
<para>Libraries like this cost in the region of $20,000, pricing them a
|
||||
little out of the hobbyist market.</para>
|
||||
</sect2>
|
||||
|
||||
<sect2>
|
||||
<title>Using a New Tape for the First Time</title>
|
||||
|
||||
<para>The first time that you try to read or write a new, completely
|
||||
blank tape, the operation will fail. The console messages should be
|
||||
similar to:</para>
|
||||
|
||||
<screen>sa0(ncr1:4:0): NOT READY asc:4,1
|
||||
sa0(ncr1:4:0): Logical unit is in process of becoming ready</screen>
|
||||
|
||||
<para>The tape does not contain an Identifier Block (block number 0).
|
||||
All QIC tape drives since the adoption of QIC-525 standard write an
|
||||
Identifier Block to the tape. There are two solutions:</para>
|
||||
|
||||
<para><command>mt fsf 1</command> causes the tape drive to write an
|
||||
Identifier Block to the tape.</para>
|
||||
|
||||
<para>Use the front panel button to eject the tape.</para>
|
||||
|
||||
<para>Re-insert the tape and <command>dump</command> data to the tape.</para>
|
||||
|
||||
<para><command>dump</command> will report <literal>DUMP: End of tape
|
||||
detected</literal> and the console will show: <literal>HARDWARE
|
||||
FAILURE info:280 asc:80,96</literal>.</para>
|
||||
|
||||
<para>rewind the tape using: <command>mt rewind</command>.</para>
|
||||
|
||||
<para>Subsequent tape operations are successful.</para>
|
||||
</sect2>
|
||||
</sect1>
|
||||
</chapter>
|
||||
|
||||
<!--
|
||||
|
|
|
|||
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Reference in a new issue