We have a need to backup both VMs (at the hypervisor level), and a large NAS used for file storage. We are a charity, and have 6 sockets to manage, and so the options that seem to have both VM and bare metal backups are out of our desired budget. (I know, this is the area to make an exception if you have to, but...trying to see what I can do without.)

I've seen/tested a couple of solid-seeming backup solutions in our budget that do exactly what we need at the VM level. However, they won't do the NAS by default. The option we've been given is to present the NAS as RDM disks to VMWare. I've tried this, and I can add the disks fine. However, when it goes to actually do the backups, things fall apart.

When any of the VM-based systems are doing a backup, they're creating a temporary snapshot. However, the hosts that the VMs are running on don't have anywhere near the space that the NAS does. (This is why we have the setup we do - fast RAIDed local drives for the VMs themselves and main file storage, and then the external NAS with slower, large drives for large media files and such.) So when it tries to take the snapshot, the host datastore gets filled, and then everything on the host gets suspended due to lack of space.

Am I missing an option here (other than paying way more for an agent-based solution as well)? For example, is there some way to make the snapshots for those NAS drives happen on the NAS, while everything for the main OS happens on the main host? I'd never heard of an RDM before this whole thing came up, so I'm still not 100% sure I have my brain wrapped around all of the possibilities.

Edited to add: I'll investigate options within the NAS to do backups with its own built-in capabilities as a fall-back plan - however, I'd love to have all the backups done through the same system if possible, and we need VM backups, so still hoping there's a way to make the disks work in terms of where/how the snapshots are stored during backup.

Looks like I could possibly make the iSCSI lun a datastore, and create regular virtual disks on it, rather than having individual RDMs. There seems to be some differing info (possibly due to a config/settings change at some point?) as to whether this would do what I need, which is for the the snapshots to be saved on the NAS with the disks rather than on the local host datastore. Investigating further, but curious if anyone has tried this or has anything definitive...

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    Telling us what make/model NAS you have would surely be helpful.
    – joeqwerty
    Commented Dec 22, 2016 at 19:45
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    Sorry - just a Synology DS414. Not anything high end/fancy. :-)
    – teleute00
    Commented Dec 22, 2016 at 20:41
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    Synology has support for a number of different backup methods (private cloud, public cloud, etc.). Have you looked into using one of them?
    – joeqwerty
    Commented Dec 22, 2016 at 20:57
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    Hmmm....honestly, I hadn't, because my preference (and so my initial investigations) is to have all backups done in the same system by the same software, so that it's all dealt with from one place with only one system to learn. It would still be my preference, but I'll look into using the Synology capabilities in addition to VM backups as a secondary option. Thanks!
    – teleute00
    Commented Dec 22, 2016 at 21:17

1 Answer 1


As far as I know, Veeam can handle with your task.


It seems that I could do ISCSI Lun data storage, and create regular virtual disks on it, rather than having individual RDMS. This idea is very useful thus the time you'll spend on a backup will be significantly reduced.

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    Veeam is out of our budget, but that general idea seems consistent with what I was speculating about in the comments above. I've been setting up some tests and it looks promising. Will report back once I've got more data.
    – teleute00
    Commented Dec 23, 2016 at 19:21
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    Veeam has a free version. Also if you're participating in VMUG they have VMUG-specific offerings from time to time. Worth going and asking IMHO. It's the best VM backup you can get these days. Commented Dec 24, 2016 at 10:22
  • There are some limitations to the free version that we're hoping to avoid (it says it only partially supported file-level restores, whatever that means - also need backup copy jobs for our offsites, scheduled jobs, and incrementals). We can get these in our budget in a few solutions, but this disk/snapshot thing is the issue with all of them. So far, though, the ISCSI datastore (instead of the RDMs) looks super promising in my testing. Don't know why none of the vendors I spoke with mentioned it instead of RDMs. :-( When you say the time spent on backups will be reduced - why?
    – teleute00
    Commented Dec 28, 2016 at 17:34

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