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Re: Help with XFS in VMs on VMFS

To: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Subject: Re: Help with XFS in VMs on VMFS
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Sun, 31 Mar 2013 13:04:49 +1100
Cc: Ben Myers <bpm@xxxxxxx>, Jan Perci <jperci@xxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <51573924.2020304@xxxxxxxxxxxxxxxxx>
References: <CAJoqCq9WhFi8yZnTjh_dJmOte4TWpKg3qsQLpVsZ45M8XoWiaA@xxxxxxxxxxxxxx> <51549F09.1090109@xxxxxxxxxxxxxxxxx> <20130328214550.GA3771@xxxxxxxxxxxxx> <5154E6AC.9020402@xxxxxxxxxxxxxxxxx> <CAJoqCq_afu4d++fgkGGMDC55pcz62V3qyai906ihQ2d=eiyhhQ@xxxxxxxxxxxxxx> <20130329202735.GX22182@xxxxxxx> <51573924.2020304@xxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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.


Dave Chinner

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