svn commit: r40676 - head/en_US.ISO8859-1/books/handbook/disks
Warren Block
wblock at FreeBSD.org
Fri Jan 18 01:17:05 UTC 2013
Author: wblock
Date: Fri Jan 18 01:17:04 2013
New Revision: 40676
URL: http://svnweb.freebsd.org/changeset/doc/40676
Log:
Update the Using Tapes section to more closely reflect modern reality.
Modified version of patch from PR.
PR: docs/175226
Submitted by: Diane Bruce <db at db.net>
Modified:
head/en_US.ISO8859-1/books/handbook/disks/chapter.xml
Modified: head/en_US.ISO8859-1/books/handbook/disks/chapter.xml
==============================================================================
--- head/en_US.ISO8859-1/books/handbook/disks/chapter.xml Thu Jan 17 22:52:01 2013 (r40675)
+++ head/en_US.ISO8859-1/books/handbook/disks/chapter.xml Fri Jan 18 01:17:04 2013 (r40676)
@@ -2085,233 +2085,93 @@ cd0: Attempt to query device size failed
<indexterm><primary>tape media</primary></indexterm>
- <para>The major tape media are the 4mm, 8mm, QIC, mini-cartridge
- and DLT.</para>
+ <para>Tape technology has continued to evolve but is less likely
+ to be used in a modern system. Modern backup systems tend to
+ use offsite combined with local removable disk drive
+ technologies. Still, FreeBSD will support any tape drive that
+ uses SCSI such as LTO and older devices such as DAT. There is
+ limited support for SATA and USB tape drives as well.</para>
- <sect2 id="backups-tapebackups-4mm">
- <title>4mm (DDS: Digital Data Storage)</title>
+ <sect2 id="tapes-sa0">
+ <title>Serial Access with &man.sa.4;</title>
<indexterm>
- <primary>tape media</primary>
- <secondary>DDS (4mm) tapes</secondary>
+ <primary>tape drives</primary>
</indexterm>
- <indexterm>
- <primary>tape media</primary>
- <secondary>QIC tapes</secondary>
- </indexterm>
- <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>
-
- <para>Data throughput on these drives starts ~150 kB/s,
- peaking at ~500 kB/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>
+ <para>FreeBSD uses the &man.sa.4; driver, providing
+ <devicename>/dev/sa0</devicename>,
+ <devicename>/dev/nsa0</devicename>, and
+ <devicename>/dev/esa0</devicename>. In normal use, only
+ <devicename>/dev/sa0</devicename> is needed.
+ <devicename>/dev/nsa0</devicename> is the same physical drive
+ as <devicename>/dev/sa0</devicename> but does not rewind the
+ tape after writing a file. This allows writing more than one
+ file to a tape. Using <devicename>/dev/esa0</devicename>
+ ejects the tape after the device is closed, if
+ applicable.</para>
</sect2>
- <sect2 id="backups-tapebackups-8mm">
- <title>8mm (Exabyte)</title>
-
- <indexterm>
- <primary>tape media</primary>
- <secondary>Exabyte (8mm) tapes</secondary>
- </indexterm>
-
- <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 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 ~250 kB/s to
- ~500 kB/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>
-
- <sect2 id="backups-tapebackups-qic">
- <title>QIC</title>
+ <sect2>
+ <title id="tapes-mt">Controlling the Tape Drive with
+ &man.mt.1;</title>
<indexterm>
<primary>tape media</primary>
- <secondary>QIC-150</secondary>
+ <secondary>mt</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 <quote>serious</quote> 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 (152 x
- 102 x 17 mm).</para>
-
- <para>Data throughput ranges from ~150 kB/s to
- ~500 kB/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-dlt">
- <title>DLT</title>
+ <para>&man.mt.1; is the &os; utility for controlling other
+ operations of the tape drive, such as seeking through files on
+ a tape or writing tape control marks to the tape.</para>
- <indexterm>
- <primary>tape media</primary>
- <secondary>DLT</secondary>
- </indexterm>
+ <para>For example, the first three files on a tape can be
+ preserved by skipping past them before writing a new
+ file:</para>
- <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 <quote>hook</quote> 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 1.5 MB/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>
+ <screen>&prompt.root; <userinput>mt -f /dev/nsa0 fsf 3</userinput></screen>
</sect2>
<sect2>
- <title id="backups-tapebackups-ait">AIT</title>
+ <title id="tapes-tar">Using &man.tar.1; to Read and
+ Write Tape Backups</title>
- <indexterm>
- <primary>tape media</primary>
- <secondary>AIT</secondary>
- </indexterm>
+ <para>An example of writing a single file to tape using
+ &man.tar.1;:</para>
- <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 <application>SAMS:Alexandria</application> 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>
+ <screen>&prompt.root; <userinput>tar cvf /dev/sa0 <replaceable>file</replaceable></userinput></screen>
- <para>Libraries like this cost in the region of $20,000, pricing
- them a little out of the hobbyist market.</para>
+ <para>Recovering files from a &man.tar.1; archive on tape into
+ the current directory:</para>
+
+ <screen>&prompt.root; <userinput>tar xvf /dev/sa0</userinput></screen>
</sect2>
<sect2>
- <title>Using a New Tape for the First Time</title>
+ <title id="tapes-dumprestore">Using &man.dump.8; and
+ &man.restore.8; to Create and Restore Backups</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>
+ <para>A simple backup of <filename
+ class="directory">/usr</filename> with &man.dump.8;:</para>
- <screen>sa0(ncr1:4:0): NOT READY asc:4,1
-sa0(ncr1:4:0): Logical unit is in process of becoming ready</screen>
+ <screen>&prompt.root; <userinput>dump -0aL -b64 -f /dev/nsa0 /usr</userinput></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>Interactively restoring files from a &man.dump.8; file on
+ tape into the current directory:</para>
- <itemizedlist>
- <listitem>
- <para><command>mt fsf 1</command> causes the tape drive to
- write an Identifier Block to the tape.</para>
- </listitem>
-
- <listitem>
- <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
- <errorname>DUMP: End of tape detected</errorname> and the
- console will show: <errorname>HARDWARE FAILURE info:280
- asc:80,96</errorname>.</para>
+ <screen>&prompt.root; <userinput>restore -i -f /dev/nsa0</userinput></screen>
+ </sect2>
- <para>rewind the tape using:
- <command>mt rewind</command>.</para>
+ <sect2>
+ <title id="tapes-othersofware">Other Tape Software</title>
- <para>Subsequent tape operations are successful.</para>
- </listitem>
- </itemizedlist>
+ <para>Higher-level programs are available to simplify tape
+ backup. The most popular are
+ <application>AMANDA</application> and
+ <application>Bacula</application>. These programs aim to make
+ backup easier and more convenient, or to automate complex
+ backups of multiple machines. The Ports Collection contains
+ both these and other tape utility applications.</para>
</sect2>
</sect1>
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