Re: Help with XFS in VMs on VMFS

[Ralf Gross <Ralf-Lists@ralfgross.de>]

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).

http://pubs.vmware.com/vsphere-51/topic/com.vmware.vsphere.storage.doc/GUID-0114693D-94BF-4D0E-9BA4-416D4A51A5A1.html
 
> 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
page.

http://blogs.vmware.com/vsphere/2013/01/vsphere-5-1-vmdk-versus-rdm.html

 
> 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.

Ralf

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