VMWare quiesced snapshots - What's the real info?

[ndemarco]

We're testing a migration from a commercial storage concentrator (StoneFly) to FreeNAS. Our resident VMWare guru is concerned about taking quiesced snapshots of the ZFS volumes. My searches for VMWare snapshot support in FreeNAS hasn't turned up much except in 8.04-BETA3, where the VMWare awareness has been reworked.

Does a FreeNAS/VMWare best practices guide exist anywhere?

 

[Brand]

Does a FreeNAS/VMWare best practices guide exist anywhere?

Not likely since FreeNAS was never intended to run in a virtual machine to the best of my knowledge.

 

[ndemarco]

That's not my use.

VMWare running on one or more boxes.
FreeNAS running on another one or more separate boxes.
The boxes are connected by a Storage Area Network (SAN).

It's common to have storage outside of the VMWare physical hardware. That's how VMotion and other High Availability products operate. If VMWare is informed a snapshot will be taken, VMWare will "quiesce" including flushing the write caches and pausing disk writes for a 'cleaner' snapshot--one that isn't changing between the time the snapshot starts and the time it ends.

So, can someone point me to some best practices for using FreeNAS as a storage concentrator for VMWare? I saw the one release note stating VMWare was quite supported, but I haven't found any detail about how the support may have been implemented.

 

[grapenuts]

That's not what quiescing refers to. It means that the file system inside the guest OS is being quiesced by the VMware Tools so that the snapshot is in theory not crash-consistent.

 

[ndemarco]

Thanks, but that restates what I said. So far, responses have been, in effect, a) FreeNAS isn't meant to be run as a VM under a hypervisor; b) Clarification on what it means to quiesce a VM. I appreciate the attempts, but the question still remains unanswered.

Can someone point me to best practices on using FreeNAS as a storage concentrator for VMWare?

 

[Letni]

Working for a big name Enterprise SAN company (E*C - you can guess) in a Business Continuance architect role, and having VCP certification, I can tell you there is going to be NO DIRECT support within FreeNAS to worth through the VM Layer (ESX - I'm assuming) to quiesce VMs on VMFS or NFS when a ZFS snap is being kicked off. Those are enterprise type features (and let me tell you enterprise is just now recently coming around to some support for this), and this is FreeNAS where were lucky to have the features we have. Be happy with your crash consistent snaps/clones and if you really need OS/application quiesced copies, your best bet is probably paying for a solution that supports that.

 

[ndemarco]

That's not the answer I was hoping for, but it does answer my question. Thanks.

We will keep playing around, perhaps with some scripting.

 

[Letni]

If you are going to attempt to script (assuming running Win2k3/2k8 with Exchange/Oracle/SQL) your path of least resistance to be able to begin to script a solution would be to utilize iSCSI LUNs directly from the guest back to FreeNAS (iSCSI initiator within the guest) for the data volumes. The other option would be to use iSCSI in the hypervisor and present RDM to the guest (also avoiding VMDK on VMFS/NFS). Both these ways will help minimize the "layers" to quiesce around. The other challenges here are to be able to provide freeze/thaw (or hotbackup) scripts for your application (since this is really what needs to be quiesced to provide a restartable copy).

Also you may find challenging FreeNAS's current function around CLI (required for scripting) staying in-sync with the GUI. You can use the ZFS CLI to create snapshots, but with current stable version of FreeNAS, they won't show up in the GUI. You will want to wait till 8.2 is out where all actions GUI or CLI will stay in-sync with each other...

Only expect so much from a free project which has slow development cycles.

Good luck as this is not going to be an easy endeavor.