Re: XFS optimization question

[Steve Lord <lord@sgi.com>]

On Tue, 2002-05-07 at 17:07, Murthy Kambhampaty wrote:
> I am having a little trouble decoding the documentation on "sunit" and
> "swidth" w.t.t. my raid controller.
> 
> Some background:
> I have a Mylex Acceleraid352 controller running a system drive in raid-5 and
> a data drive in raid-0. The default stripe width on the controller is 64K,
> and a segment size of 8k, and this is what the driver's documentation says
> about configuring ext2 filesystems:
> 
> "For maximum performance and the most efficient E2FSCK performance, it is
> recommended that EXT2 file systems be built with a 4KB block size and 16
> block stride to match the DAC960 controller's 64KB default stripe size.  The
> command "mke2fs -b 4096 -R stride=16 <device>" is appropriate."
> 
> For XFS, I haven't been able to find sufficient information to figure out
> whether it is sunit or swidth that is analagous to the "stride" or "stripe
> width" of 64K? It sounds to me like swidth, in which case would sunit be set
> to the segment size of 8k?
> 
> I'm probably going over ground that's been covered previously on this list,
> but didn't have much luck finding it in the archive or the documentation.
> 
> Thanks for the help,
> 	Murthy

I would guess from your description of the DAC960 that in xfs terms, the
stripe width is 64K and the stripe unit is 8K. To quote from the mkfs.xfs
man page:

              The sw suboption is an alternative to using swidth.
              The  sw  suboption  is  used  to specify the stripe
              width for a RAID device or striped logical  volume.
              The suboption value is expressed as a multiplier of
              the stripe unit, usually the same as the number  of
              stripe members in the logical volume configuration,
              or data disks in a RAID device.

However, the stripe width is truly more closely related to how many disks
you have in a striped volume. Who knows what the DAC960 is really doing with
that number. Most things though are based on stripe unit, and 8K does
sound correct for that.

I would get the latest mkfs from cvs, some changes just went in which
relate to how striped filesystems are aligned.

Steve


-- 

Steve Lord                                      voice: +1-651-683-3511
Principal Engineer, Filesystem Software         email: lord@sgi.com