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Re: Help with XFS in VMs on VMFS

To: xfs@xxxxxxxxxxx
Subject: Re: Help with XFS in VMs on VMFS
From: Ralf Gross <Ralf-Lists@xxxxxxxxxxxx>
Date: Thu, 28 Mar 2013 22:45:50 +0100
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In-reply-to: <51549F09.1090109@xxxxxxxxxxxxxxxxx>
References: <CAJoqCq9WhFi8yZnTjh_dJmOte4TWpKg3qsQLpVsZ45M8XoWiaA@xxxxxxxxxxxxxx> <51549F09.1090109@xxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
Stan Hoeppner schrieb:
> On 3/28/2013 8:21 AM, Jan Perci wrote:
> > Normally I would use raw mappings and XFS directly on the volumes.  But
> > there is a hard requirement to support VM snapshots, so all the data must
> > reside within VMDK files on the VMFS datastores.
> Since when?  ESX has had LUN snapshot capability back to 3.0, 6 years or
> so.  It may have required the VCB add on back then.

Snapshots are possible with RDM in virtual compatibily mode, not
physical mode (> 2 TB).

> Is this simply a limitation of the freebie version?  If so, pony up and
> pay for what you need, or switch to a FOSS solution which has no such
> limitations.

No, thats the limit for all versions.

> VMFS volumes are not intended for high performance IO.  Unless things
> have changed recently, VMware has always recommended housing only OS
> images and the like in VMDKs, not user data.  They've always recommended
> using RDMs for everything else.  IIRC VMDKs have a huge block (sector)
> size, something like 1MB.  That's going to make XFS alignment difficult,
> if not impossible.

I can't remember that I've every found this recommendation on a vmware


> I cannot stress emphatically enough that you should not stitch 2TB VMDKs
> together and use them in the manner you described.  This is a recipe for
> disaster.  Find another solution.

I'm seeing more and more requests for VMs with large disks lately in my
env. Right now the max. is ~2 TB. I'm also thinking about where to go,
 > 2 TB ist only possible with pRDMs which can't be snapshotted. You
have to use the snapshot features of your storage array.


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