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Additional information about DDS-3, 8mm, DLT, and AIT capacities. Prose

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is a little stilted, which is my fault.  This section really needs rewriting
with tables of tape types, capacities, and so on, which would present the
information much more intuitively.

Submitted by:   Adam Steffes <asteffes@ucdavis.edu>
This commit is contained in:
Nik Clayton 1999-10-26 21:39:59 +00:00
parent e63934d6ca
commit ce64e9b1c4
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=5945
2 changed files with 58 additions and 2 deletions
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30
en_US.ISO8859-1/books/handbook/backups/chapter.sgml
View file

@ -1,7 +1,7 @@
<!--
The FreeBSD Documentation Project
$FreeBSD: doc/en_US.ISO_8859-1/books/handbook/backups/chapter.sgml,v 1.11 1999/09/06 06:52:53 peter Exp $
$FreeBSD: doc/en_US.ISO_8859-1/books/handbook/backups/chapter.sgml,v 1.12 1999/09/10 00:56:44 jim Exp $
-->
<chapter id="backups">
@ -55,6 +55,9 @@
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 12GB (or
24GB 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>
@ -79,6 +82,10 @@
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 &ldquo;Mammoth&rdquo; model supports 12GB on one tape
(24MB 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
@ -150,12 +157,33 @@
tapes over 1 to 20 drives, providing from 50GB to 9TB of
storage.</para>
<para>With compression, DLT Type IV format supports up to 70GB
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>
<para>AIT is a new format from Sony, and can hold up to 50GB (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 where 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>

30
en_US.ISO_8859-1/books/handbook/backups/chapter.sgml
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@ -1,7 +1,7 @@
<!--
The FreeBSD Documentation Project
$FreeBSD: doc/en_US.ISO_8859-1/books/handbook/backups/chapter.sgml,v 1.11 1999/09/06 06:52:53 peter Exp $
$FreeBSD: doc/en_US.ISO_8859-1/books/handbook/backups/chapter.sgml,v 1.12 1999/09/10 00:56:44 jim Exp $
-->
<chapter id="backups">
@ -55,6 +55,9 @@
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 12GB (or
24GB 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>
@ -79,6 +82,10 @@
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 &ldquo;Mammoth&rdquo; model supports 12GB on one tape
(24MB 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
@ -150,12 +157,33 @@
tapes over 1 to 20 drives, providing from 50GB to 9TB of
storage.</para>
<para>With compression, DLT Type IV format supports up to 70GB
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>
<para>AIT is a new format from Sony, and can hold up to 50GB (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 where 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>