xfs_fsr, sunit, and swidth

[Dave Chinner]

On Wed, Mar 13, 2013 at 02:11:19PM -0400, Dave Hall wrote:
> Does xfs_fsr react in any way to the sunit and swidth attributes of
> the file system?

Not directly.

> In other words, with an XFS filesytem set up
> directly on a hardware RAID, it is recommended that the mount
> command be changed to specify sunit and swidth values that reflect
> the new geometry of the RAID.

The mount option does nothing if sunit/swidth weren't specified at
mkfs time. sunit/swidth affect the initial layout of the filesystem,
and that cannot be altered after the fact. Hence you can't
arbitrarily change sunit/swidth after mkfs - you are limited to
changes that are compatible with the existing alignment. If you have
no alignment specified, then there isn't a new alignment that can be
verified as compatible with the existing layout.....

> In my case, these values were not
> specified on the mkfs.xfs of a rather large file system running on a
> RAID 6 array.

Which means the mount option won't work.

> I am wondering adding sunit and swidth parameters to
> the fstab will cause xfs_fsr to do anything different than it is
> already doing.  Most importantly, will it improve performace in any
> way?

It will make no difference at all.

A more important question: why do you even need to run xfs_fsr?

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com