Re: Did I make a mistake?

[Roman Mamedov <rm@romanrm.ru>]

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On Thu, 19 May 2011 21:45:23 -0500
"Leslie Rhorer" <lrhorer@satx.rr.com> wrote:

> 	OK, I may have made an error, and I want to make sure before this
> goes any further.  Yesterday I created a RAID6 volume with eight 3TB
> members, on the same machine containing an older RAID6 array built of
> fourteen 1G members.  Based upon my reading here and some level of
> experience with larger stripe sizes, I decided to create the array with a
> chunk size of 4096K.

4096K is an absurdly large chunk for such RAID5/RAID6 array, I wanted to refer
some benchmarks, but couldn't even find any that would test such a huge chunk,
largest they test is 1024 or 2048, where the write performance already drops
off very sharply, e.g. see:

http://blog.jamponi.net/2008/07/raid56-and-10-benchmarks-on-26255_10.html
http://louwrentius.blogspot.com/2010/05/raid-level-and-chunk-size-benchmarks.html

While the read performance does seem to not suffer or even increase at
higher chunk size, the best read/write combination performance seems to be
achieved at 64...256K chunk for RAID5/6.

If you decide to persist with the current configuration, make sure you
increase stripe_cache_size by a lot (and btw raising it if you have the
RAM to spare is a good idea in any case).

-- 
With respect,
Roman

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