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Add rudimentary section on gjournal(8), currently commented out but here as

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a documented feature for 7.X release.

Sponsored by:	AiNET Corp.
This commit is contained in:
Tom Rhodes 2007-04-18 10:00:27 +00:00
parent 55efe30995
commit cbe49e9324
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=30064
1 changed files with 87 additions and 0 deletions

87
en_US.ISO8859-1/books/handbook/geom/chapter.sgml
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@ -447,6 +447,93 @@ OK? <userinput>boot</userinput></screen>
unmounted with the &man.umount.8; command, similar to any other
disk device.</para>
</sect1>
<!--
<sect1 id="geom-gjournal">
<title>UFS Journaling Through GEOM</title>
<indexterm>
<primary>GEOM</primary>
</indexterm>
<indexterm>
<primary>Disk Mirroring</primary>
</indexterm>
<para>With the release of &os;&nbsp;7.0, the long awaited feature
of <acronym>UFS</acronym> journals has been implemented. The
implementation itself is provided through the
<acronym>GEOM</acronym> subsystem and is easily configured
via the &man.gjournal.8; utility.</para>
<para>What is journaling? Journaling capability stores a log of
file system transactions, i.e.: changes that make up a complete
disk write operation, before meta-data and file writes are
committed to the disk proper. This transaction log can later
be replayed to redo file system transactions, preventing file
system inconsistencies.</para>
<para>This method is yet another mechanism to protect against data
loss and inconsistencies of the file system. Unlike Soft Updates
which tracks and enforces meta-data updates and Snapshots which
is an image of the file system, an actual log is stored at the
end sector and, in some cases, may be stored on another disk
entirely.</para>
<para>Unlike other file system journaling implementations, the
<command>gjournal</command> method is block based and not
implemented as part of the file system - only as a
<acronym>GEOM</acronym> extension.</para>
<para>To enable support for <command>gjournal</command>, the
&os; kernel must have the following option - which is the
default on 7.X systems:</para>
<programlisting>options UFS_GJOURNAL</programlisting>
<para>Creating a journal on a free file system may now be done
using the following steps, considering that the
<devicename>da4</devicename> is a new <acronym>SCSI</acronym>
disk:</para>
<screen>&prompt.root; <userinput>gjournal label /dev/da4</userinput>
<userinput>gjournal load</userinput></screen>
<para>At this point, there should be a
<devicename>/dev/da4</devicename> device node and a
<devicename>/dev/da4.journal</devicename> device node. A
file system may now be created on this device:</para>
<screen>&prompt.root; <userinput>newfs -O 2 -J /dev/da4.journal</userinput></screen>
<para>The previously issued command will create a
<acronym>UFS</acronym>2 file system with journaling being made
active.
<para>Effectively <command>mount</command> the device at the
desired point with:</para>
<screen>&prompt.root <userinput>mount /dev/da4.journal /mnt</userinput></screen>
<note>
<para>In the case of several slices, a journal will be created
for each individual slice. For instance, if ad4s1 and ad4s2
are both slices, then <command>gjournal</command> will create
ad4s1.journal and ad4s2.journal. In the case of the command
being run twice, the result will be
<quote>journals</quote>.</para>
</note>
<para>Under some circumstances, keeping the journal on another disk
may be desired. For these cases, the journal provider or storage
device should be listed after the device to enable journaling
on. Journaling may also be enabled on current file systems by
using <command>tunefs</command>; however, always make a backup
before attempting to alter a file system. In most cases, the
<command>gjournal</command> will fail if it is unable to create
the actual journal but this does not protect against data loss
incurred as a result of misusing
<command>tunefs</command>.</para>
</sect1>
-->
</chapter>
<!--