>>>>> "Steve" == Stephen Lord <lord@xxxxxxx> writes:
>> The XFS FAQ says that XFS performs slightly worse than ext2 on Soft
>> RAID1 and RAID5.
Hrm, I wonder why it says RAID1. RAID1 doesn't have a stripe cache
and consequently doesn't suffer.
I think the RAID1 comment may be a leftover from when I switched MD
from 1K to 512 byte resyncs and had problems with the throttling.
In any case, I think we should remove RAID1 from the caveat.
>> XFS on Hardware RAID5 w/o write caching : ~10 min XFS on Hardware
>> RAID5 w write caching : ~13 min EXT3 on Hardware RAID5 w/o write
>> caching : ~13 min XFS on Software RAID5 w/o write caching : ~42 min
>> EXT3 on Software RAID5 w/o write caching : ~12 min XFS on Software
>> RAID5 w/o write caching, logdev on SoftRAID1 on the same disks :
>> ~10 min
Simon:
Hrm, nasty. Did you let the RAID5 device finish resync before use?
With both XFS and the resync messing with the stripe cache,
performance is bound to suffer bigtime.
Steve> We have talked about adding some padding to the log, but it is
Steve> an on disk format change, so not something to do lightly, if I
Steve> find time I may do some experiments with it.
Another option (which could potentially also help XFS on mainframes
with 4K hardware sectors) is to have a slim layer do read-modify-write
on fixed size chunks between the fs and RAID5.
--
Martin K. Petersen, Principal Linux Consultant, Linuxcare, Inc.
mkp@xxxxxxxxxxxxx, http://www.linuxcare.com/
SGI XFS for Linux Developer, http://oss.sgi.com/projects/xfs/
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