On Sun, 25 Jul 2010 14:58:37 +0000 (GMT)
Marco [off-list ref] wrote:

doing a simple performance tests i obtained some very unexpected results: if
i issue hdparm -t /dev/md2 i obtain 61 - 65 MB/s while issuing the same test 
directly on the partitions which compose md2 (/dev/sda3 and /dev/sdb3) i
obtain 84 - 87 MB/s. I didn't expect a so big difference between md2 and one
of its member. What can cause  this difference ? 

Maybe their read-ahead settings are different?
Check out "blockdev --getra /dev/md2", and compare that with the same
setting of the member disks. You can experiment with changing it by using
"--setra" as well.

-- 
With respect,
Roman