Date: Thu, 3 Oct 2013 11:44:38 -0400 (EDT) From: Benjamin Kaduk <kaduk@MIT.EDU> To: Benedict Reuschling <bcr@freebsd.org> Cc: svn-doc-projects@freebsd.org, doc-committers@freebsd.org Subject: Re: svn commit: r42810 - projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/zfs Message-ID: <alpine.GSO.1.10.1310031139520.16692@multics.mit.edu> In-Reply-To: <201310022100.r92L07qP038968@svn.freebsd.org> References: <201310022100.r92L07qP038968@svn.freebsd.org>
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On Wed, 2 Oct 2013, Benedict Reuschling wrote: > Author: bcr > Date: Wed Oct 2 21:00:07 2013 > New Revision: 42810 > URL: http://svnweb.freebsd.org/changeset/doc/42810 > > Log: > Add a section on deduplication. This needs some more work and warnings about > huge memory requirements for the DDT. But the basic instructions are there on > how to activate it, along with an example that shows the dedup ratio and > a simulation run with zdb. > > Modified: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/zfs/chapter.xml > ============================================================================== > --- projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/zfs/chapter.xml Wed Oct 2 20:02:02 2013 (r42809) > +++ projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/zfs/chapter.xml Wed Oct 2 21:00:07 2013 (r42810) > + > + <para>The <literal>DEDUP</literal> column shows the actual rate > + of deduplication for that pool. A value of > + <literal>1.00x</literal> that no data has been deduplicated > + due to insufficient duplicate data. In the following example, > + the ports tree is copied three times into different > + directories on the deduplicated pool above to provide > + redundancy.</para> I'm not sure that this is the best way to talk about an example use-case where deduplication would come into play. If the user actually wants redundancy (that is, to ensure that there is a reliable/correct copy of the ports tree around in the event of hardware issues), deduplication is not the right tool, 'zfs set -o copies=3' would be more appropriate. The whole point of the deduplication is that there is only one actual copy on disk. It would probably be a better example to talk about copying the ports tree three different times for testing different configurations or something like that. -Ben > + <screen>&prompt.root; <userinput>zpool list</userinput> > +for d in dir1 dir2 dir3; do > +for> mkdir $d && cp -R /usr/ports $d & > +for> done</screen> > + > + <para>Now that redundant data has been created, ZFS detects that > + and makes sure that the data is not taking up additional > + space.</para>
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