xfs
[Top] [All Lists]

Re: write-caching with XFS

To: Stephen Lord <lord@xxxxxxx>
Subject: Re: write-caching with XFS
From: "Martin K. Petersen" <mkp@xxxxxxxxxxxxx>
Date: 08 Jan 2002 08:49:39 -0500
Cc: Simon Matter <simon.matter@xxxxxxxxxxxxxxxx>, Chris Parrott <chris.parrott@xxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: <3C3AE709.30701@xxxxxxx>
Organization: Linuxcare, Inc.
References: <3C39DADF.8010700@xxxxxxxxxxxx> <1010430010.7120.45.camel@xxxxxxxxxxxxxxxxxxxx> <3C3A9C32.123DA48@xxxxxxxxxxxxxxxx> <3C3AE709.30701@xxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
User-agent: Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.4 (Civil Service)
>>>>> "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/


<Prev in Thread] Current Thread [Next in Thread>