Re: performance problems with raid10,f2

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I have a 4 drive array with 1 TB Hitachi disks, formatted
as raid10,f2 I had some strange observations: 1. while
resyncing I could get the raid to give me about 320 MB/s in
sequential read, which was good. After resync had been
done, and with all 4 drives active, I only get 115 MB/s.

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Is this with, or without, your patch to avoid "read-balancing"
for raid10/far layouts?  It sounds like it is without that
patch ????

I tried both without the patch and with the patch, with almost
same resulte.

That could be the usual issue with apparent pauses in the stream
of IO requests to the array component devices, with the usual
workaround of trying 'blockdev --setra 65536 /dev/mdN' and see if
sequential reads improve.

Is resync building some table, and could that be it?  Or could
it be some time of inode traffic?

One good way to see what is actually happening is to use either
'watch iostat -k 1 2' and look at the load on the individual MD
array component devices, or use 'sysctl vm/block_dump=1' and look
at the addresses being read or written.