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This question is two fold.

Part 1:

Is it a bad idea to virtualize a storage solution and run VMDKs off of that as opposed to the original VMFS datastore.

Essentially lets assume I have 2 TB worth of RAID'd DAS. Currently I have a few VMDKs on the DAS VMSFS. What I want to do is remove the VMDKs off the VMFS, allocate a good 1.8-1.9TB for a FreeNAS installation (a big FreeNAS VMDK), and run the other VMDKs off of that via NFS.

I don't have the hardware for a NAS but have a bunch of different shares. This would simplify my management. I understand there is some overhead with another layer of storage abstraction (A virtual ZFS file system over NFS backed by RAID'd DAS formatted as VMFS) but I don't see how it could be too bad. The NAS also has more features than a simple VMFS datastore on DAS.

Part 2:

VMWare frowns on long running snapshots, but what about ZFS snapshots? Is it safe\recomended to run my guest VMDKs (Windows clients, random servers) on ZFS snapshots? This will give me the ability to quickly rollback VMs to earlier states without the implications of long running snapshots directly on the VMFS.

VM_Storage_Inception
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    Your name says it all. There is risk inherent in counting on anything that is set up in such a way that the storage that VMWare counts on runs inside a VM in that same hypervisor. Unless I'm misunderstanding Part 1. – Craig Nov 25 '14 at 15:24
  • You are understanding part1 right. I essentially want to run VMDKs (guests) inside of another VMDK (the FreeNAS install). I've read of virtualized storage before, just on a different physical box. I've also read about VMDKs over NFS on a NAS. In both of these cases you still have the VMDks depending on another solution – VM_Storage_Inception Nov 25 '14 at 15:27
  • Right, the part that sets them apart is being on a different physical box, at least in that way you can control the failure to some degree. – Craig Nov 25 '14 at 15:32
  • I see your point. This is for a lab and I am on a budget but here's what I see. If the DAS dies I am screwed anyway whether it be FreeNAS or directly on the VMFS. If the FreeNAS install dies I would be screwed anyway whether this be a separate box or the same box. The points of failure are still the same, I just have less redundancy. – VM_Storage_Inception Nov 25 '14 at 15:36
  • Ahh, thanks for the clarification. Lab setups, of course, are exempt from most of my concerns. – Craig Nov 25 '14 at 15:43
  • Have you considered using VSAN or VSA? – Chopper3 Nov 25 '14 at 16:15
  • Generally you would map the raw disks to the storage VM and reshare it rather than have them sitting on vmfs. Are you aware of the sync write issues of using NFS, this requires SSDs/flashram products for the writelog to give any decent performance. – JamesRyan Nov 25 '14 at 17:07
  • @JamesRyan - FreeNAS can present itself as an iSCSI SAN. – VM_Storage_Inception Nov 25 '14 at 18:12
  • @Chopper3 - isn't that what VSAN essentially is? A big VMDK installed on your ESXI box that runs the VSAN image which then stores your other VMDKs – VM_Storage_Inception Nov 25 '14 at 18:12
  • This has been done before.. it's not a good solution unless you're running a support VSA-type appliance (like HP's VSA). If doing this, I would NOT recommend FreeNAS. Nowadays, VMware's vSAN is integrated at a deeper level. But really, if not doing one of the above, running storage inside your hypervisor is messy and fraught with risk. – ewwhite Nov 25 '14 at 23:06
  • @VM_Storage_Inception - yes, but it's supported – Chopper3 Nov 26 '14 at 09:13
  • @VM_Storage_Inception if you use iscsi not honouring sync writes you can suffer data loss, honouring them you get the same latency issue as with nfs. Its just a different default. There is no free lunch. – JamesRyan Nov 26 '14 at 10:57

2 Answers2

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For a lab environment there's nothing wrong with Part 1, other than the time spent rebuilding when it folds in on itself. Not saying it's will happen, just that it can happen (Murphy's Law).

As to Part 2, I'd have to defer to VMWare.

Craig
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  • What do you mean defer to VMWare? As in use the DAS? My theory about running VMs over a NAS (Virtualized or physical) is to take advantage of ZFS and it's snapshots. I could always snapshot the VMDKs but VMWare frowns on that. I see blogs where people snapshot their NAS just fine and no one bats an eye. – VM_Storage_Inception Nov 25 '14 at 15:58
  • As to the use of the ZFS snapshots. Again, it's a lab environment, so the risk is minimal. – Craig Nov 25 '14 at 16:13
  • but what about production environments. Would you run VMs on ZFS snapshots assuming a dedicated FreeNAS (or other NAS) box? – VM_Storage_Inception Nov 25 '14 at 16:48
  • Well, this is getting into pure opinion, but having worked on production environments from as small as one server to thousands of servers, I'd never want to depend on the ZFS snapshots to work, not if users were depending on those systems services to be online. ZFS is not a panacea. There are a lot of things that seem elegant or even fun that are just a bad idea in a production environment. – Craig Nov 25 '14 at 16:53
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    ZFS is well established, several leading mainstream san products are based on it. That doesn't mean that a haphazard installation of it will be fine. Also ZFS snapshots are not a copy, you need to be doing replication too. – JamesRyan Nov 25 '14 at 17:03
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I don't know about part 2 but for part 1:

Actually, both VMware and HP offer products to do this: VMware VSA and HP VSA. (There might be others offering similar solutions but those are the two I know of.) So it's probably not a generally bad idea. However, I don't know if FreeNAS is an officially supported storage solution so you might lack support when there are problems with it. Without support I wouldn't run it in production. But since you want to deploy it in a lab environment you have to decide for yourself if you can do without support.

There might (just might) be a certain impact as described here. (It's about a flash virtualization platform but the basics of kernel module versus virtual appliance should apply to virtual storage appliances, too.) On the other hand, it's possible you won't experience any performance issues.

Mario Lenz
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  • I'm not a big believer in support anyway ;). But ya, that's what I thought VSAN was. Just a Virtual SAN (big VMDK) where you can store things, including other VMs (little VMDKs) – VM_Storage_Inception Nov 25 '14 at 21:10
  • @VM_Storage_Inception I'm not a big believer in support either, but sometimes it *is* helpful; especially in a production environment. Btw: I wasn't talking about VSAN. That's something completely different because it's *not* a virtual storage appliance, it's built into vSphere: http://cormachogan.com/2013/09/03/vsan-part-3-it-is-not-a-virtual-storage-appliance/ It solves (more or less) the same problems as a virtual storage appliance, though. – Mario Lenz Nov 26 '14 at 19:43