On Fri, Jun 16, 2006 at 05:27:14PM -0400, Justin Piszcz wrote:
> Two questions, a SW RAID and XFS question.
>
> SW RAID Question: What is the optimal chunk size for a RAID5 that will be
> used with XFS?
The answer to that is "it depends". It depends on workload, file sizes,
write patterns, etc. There is no magic number that will give you the
best performance in all cases.
> I have 5x400GB Seagate HDDs (ATA/100) w/ 8MB of Cache,
> each is a master on its own IDE bus.
...
> I have a software raid5 with 5 400GB drives and currently a 512kb
> chunksize with default mkfs.xfs parameters.
>
> p34:~# mdadm --create /dev/md3 --verbose --chunk=512 --level=5
> --raid-devices=5 /dev/hda1 /dev/hde1 /dev/hdg1 /dev/hdi1 /dev/hdk1
> mdadm: layout defaults to left-symmetric
> mdadm: size set to 390708736K
> mdadm: array /dev/md3 started.
> p34:~#
>
> What parameters for the sunit/sw are optimal for my configuration? How
> exactly do I calculate them?
stripe unit = MD chunk size
stripe width = MD Chunk size * number of data disks in stripe (N-1 for RAID5)
Cheers,
Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group
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