Re: Issue with RHEL6 mkfs.xfs (3.1.1+), HP P420 RAID, and MySQL replication

Dave Chinner
2015-07-10T22:42:40Z

On Fri, Jul 10, 2015 at 03:59:48PM +0000, Hogan Whittall wrote:
> Hi Dave,
>
> Thanks for the reply, we can certainly try with the smaller log,
> but IIRC the performance hit wasn't because the disks were busy,
> it was the controller itself trying to determine what changed and
> then write that to disk.

That makes no sense to me - the controller is almost never the IO
limitation in a hardware RAID when random small IO is being issued
by the host.

> Smaller anything should help the
> controller be able to cope better, but that's not really a
> solution.
>
> Doing disk write performance tests on these systems produce very
> different results, they are capable of much more I/O than what was
> being triggered with this issue.
>
> Back to why I think this should be considered a bug, by 2.9.6
> setting 0 as the default for sunit/swidth and 3.1.1 having no way
> to set 0 for sunit/swidth the newer versions behave differently

False:

# man mkfs.xfs
....
noalign
This option disables automatic geometry detection
and creates the filesystem without stripe geometry
alignment even if the underlying storage device
provides this information.

IOWs:

# mkfs.xfs -d noalign ....

Will do exactly what you want. Or alternatively:

# mkfs.xfs -d sunit=0,swidth=0 ....

Or perhaps just turning of log stripe unit alignment will be enough:

# mkfs.xfs -l sunit=1 ....

Cheers,

Dave.