[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


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>