XFS: Abysmal write performance because of excessive seeking (allocation groups to blame?)

[Stan Hoeppner]

On 4/8/2012 4:45 PM, Emmanuel Florac wrote:
> Le Sun, 08 Apr 2012 15:33:01 -0500 vous écriviez:
> 
>>>
>>> From my experience, with modern arrays don't make much of a
>>> difference. I've reached decent IOPS (i. e. about 4000 IOPS) on
>>> large arrays of up to 46 drives provided there are enough threads
>>> -- more threads than spindles, preferably.  
>>
>> Are you speaking of a mixed metadata/data heavy IOPS workload similar
>> to that which is the focus of this thread, or another type of
>> workload?  Is this 46 drive array RAID10 or RAID6?
> 
> Pure random access, 8K IO benchmark (database simulation). RAID-6
> performs about the same in pure reading tests, but stinks terribly at
> writing of course.

In your RAID10 random write testing, was this with a filesystem or doing
direct block IO?  If the latter, I wonder if its write pattern is
anything like the access pattern we'd see hitting dozens of AGs while
creating 10s of thousands of files.

-- 
Stan