Date: Wed, 11 Jul 2012 08:49:04 -0500 (CDT) From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> To: Jason Usher <jusher71@yahoo.com> Cc: freebsd-fs@freebsd.org Subject: Re: vdev/pool math with combined raidzX vdevs... Message-ID: <alpine.GSO.2.01.1207110829540.27589@freddy.simplesystems.org> In-Reply-To: <1341992974.53118.YahooMailClassic@web122503.mail.ne1.yahoo.com> References: <1341992974.53118.YahooMailClassic@web122503.mail.ne1.yahoo.com>
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On Wed, 11 Jul 2012, Jason Usher wrote: > > Thanks for responding. So I must be mistaken, and the failure > probability of each vdev is not additive ? As I mentioned earlier > in the thread, I am not a probability person, nor would I trust my > own calculations if I tried. The probabilty is indeed additive just as you say. My point is that the fundamental integrity is offered at the vdev level. If a vdev fails, then the whole pool is gone. The MTTDL calculations for various vdev topologies vary by orders of magnitude, which tends to make the additive nature of more vdevs insignificant. Here are some useful blog articles about MTTDL: https://blogs.oracle.com/relling/entry/raid_recommendations_space_vs_mttdl http://blog.richardelling.com/2010/02/zfs-data-protection-comparison.html http://www.servethehome.com/raid-reliability-failure-anthology-part-1-primer/ Bob -- Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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