Disappointing performance of copy (MD raid + XFS)

[Eric Sandeen]

Kasper Sandberg wrote:
> On Fri, 2009-12-11 at 14:26 +1100, Dave Chinner wrote:
>> On Fri, Dec 11, 2009 at 02:41:32AM +0100, Asdo wrote:
>>> I have checked the other problem I had which I was mentioning, that I  
> <snip>
>>> Also with noalign and rotorstep at 255 the stripe_cache_size stays  
>>> usually in the lower half (below 16000 out of 32000) while with defaults  
>>> it's stuck for most of the time at the maximum and processes are stuck  
>>> sleeping in MD locks for this reason.
>> That really does sound like a misaligned filesystem - the stripe
>> cache will grow larger the more RMW cycles that need to be
>> performed...
> Sorry to interrupt, I would very much like to see if my array/xfs is
> properly aligned and all that stuff which has been mentioned inhere,
> could any of you please post the things required to check? filesystem is
> straight on md raid6, debian lenny.
> 
> 
> <snip>
> 

use xfs_info on your mountpoint, and compare the stripe unit and width
to what md tells you.  xfs_info stripe unit/width output is in fs blocks
units.

-Eric