svn commit: r40676 - head/en_US.ISO8859-1/books/handbook/disks

Warren Block wblock at
Fri Jan 18 01:17:05 UTC 2013

Author: wblock
Date: Fri Jan 18 01:17:04 2013
New Revision: 40676

  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>


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 &;</title>
-	<primary>tape media</primary>
-	<secondary>DDS (4mm) tapes</secondary>
+	<primary>tape drives</primary>
-      <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 &; 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 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
+	&;</title>
 	<primary>tape media</primary>
-	<secondary>QIC-150</secondary>
+	<secondary>mt</secondary>
-      <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>&; 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>
-      <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>
-      <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>

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