On Sun, 18 Jul 2010 17:32:25 -0700
Konstantin Svist [off-list ref] wrote:

I looked around and found that chunk size 
of 512 should work better.

Not true, at least with RAID5/6 a chunk size of 64K performs faster, see
http://louwrentius.blogspot.com/2010/05/raid-level-and-chunk-size-benchmarks.html
http://alephnull.com/benchmarks/sata2009/chunksize.html

-- 
With respect,
Roman