Re: Confusion with setting up new RAID6 with mdadm

[Roman Mamedov <roman@rm.pp.ru>]

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On Mon, 15 Nov 2010 09:13:26 +1100
Neil Brown <neilb@suse.de> wrote:

> Depending on which version of mdadm you are using, the default chunk size
> will be 64K or 512K.  I would recommend using 512K even if you have an older
> mdadm.  64K appears to be too small for modern hardware, particularly if you
> are storing large files.

According to some benchmarks I found, 64 or 128K still provide the sweet-spot
performance on RAID5 and RAID6, especially on writes.
http://louwrentius.blogspot.com/2010/05/raid-level-and-chunk-size-benchmarks.html
http://blog.jamponi.net/2008/07/raid56-and-10-benchmarks-on-26255_10.html#raid-5-performance
http://alephnull.com/benchmarks/sata2009/chunksize.html

> I agree with what Mikael and Luca suggested - particularly the suggested for
> "--bitmap internal".  You really want that.

It will also help to increase the --bitmap-chunk value to reduce its
performance impact, I suggest using 131072 or more.

-- 
With respect,
Roman

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