Re: How to boost performance

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

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On Wed, 16 Jun 2010 18:23:36 -0400
aragonx@dcsnow.com wrote:

> Before I start spewing server information, my question is this.  Is there
> anything I can tweak to improve my performance?  It seems that the server
> is CPU bound when I am transferring large amounts of data to or from it. 
> Any suggestions will be considered.  Faster processor, switching to RAID
> 0, etc.  I'm hoping there is something I can do with the RAID software
> though.  Maybe a different chunk size or different algorithm?

Increasing stripe cache size from the default of 256 should help immensely.

echo 16384 > /sys/block/md0/md/stripe_cache_size

Be warned that this consumes (^that amount * 4096 * number of disks) bytes of
RAM. Some benchmarks: 

http://peterkieser.com/2009/11/29/raid-mdraid-stripe_cache_size-vs-write-transfer/

On a related note -- Neil, are there plans to implement a stripe cache which
would be shared between all RAID devices? I have two RAID5s in my system, and
when one has a lot of writes, the other is often idle (or vice versa), so that
array's stripe cache is just sitting there wasting memory. Would be nice to
be able to have a shared pool of RAM for stripe-caching all the arrays and
the active one(s) using it to the fullest.

-- 
With respect,
Roman

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