Help with XFS in VMs on VMFS

[Dave Chinner]

On Sat, Mar 30, 2013 at 02:12:36PM -0500, Stan Hoeppner wrote:
> On 3/29/2013 3:27 PM, Ben Myers wrote:
> > Hi Jan,
> > 
> > On Thu, Mar 28, 2013 at 11:30:01PM -0400, Jan Perci wrote:
> >> Back to XFS, in this context, is there any benefit in tuning some
> >> parameters to get better performance, or will it all just be overshadowed
> >> by poor performance of the VMDKs that tuning isn't worthwhile?
> > 
> > At least get your stripe unit and width correct.
> > http://xfs.org/index.php/XFS_FAQ#Q:_How_to_calculate_the_correct_sunit.2Cswidth_values_for_optimal_performance
> 
> Is this really a good idea given that XFS sits atop a virtual disk which
> consists of multiple concatenated 2TB sparse files sitting on the VMFS
> filesystem, which, IIRC, has a 1MB sector size?  Thus can one rely on
> XFS being able to properly align to the physical RAID stripe, even if
> the math is done 'properly' (if that's even possible here)?

No, because VMFS doesn't do any specific alignment to the underlying
storage geometry.

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com