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We've got two Hyper-V hosts running multiple VMs (all flavors of Windows Servers). One of the VMs is running MS Data Protection Manager 2010, which runs beautifully (most of the time) and is connected to a separate NAS via iSCSI for the DPM storage.

I noticed when I installed the DPM agent on the Hyper-V hosts, it enumerates the VMs in the DPM Protection listing. I don't want to burn through my storage space too fast with duplicate protection, so I was wondering:

Is it recommended to back up VMs through the host, or is it better to install the DPM agent on each VM and backup as I would any other machine?

It would seem as though most people (currently including me) do it the second way, but is there any advantage to including the entries under HyperV (Backup using Child Partition Snapshop)?

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up vote 1 down vote accepted

Backing up through the host is your best bet, it'll likely be cheaper for licensing (not that DPM licenses cost that much, at least compared to other vendors) and it'll give you the ability to backup non-Windows VMs as well, though they will not backup live (they will save state, snapshot, and resume.)

One thing to be wary of is that DPM uses dynamic disks for its storage, and dynamic disks over iSCSI are not supported, last I checked. There are known issues with dynamic disks and iSCSI, which I won't go into but you should be able to find online.

Keep in mind running DPM in a VM means restoring your system or doing disaster recovery could be tricky.

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We're an academic institution -- license costs are dirt cheap :) I was wondering if there's anything official from MS on this. With DPM 2010 (and the latest hotfixes for dynamic disks), I haven't seen any issues with dynamic disks over iscsi. The reports I saw when I googled looked to be linked to people with drobo boxes. So far, my 8tb Synology box is working beautifully. – atmarx Feb 25 '11 at 21:18
The issue with dynamic disks and iSCSI was fixed in Windows 2008. – icky3000 Feb 25 '11 at 22:22
Re: Icky, the issues I've heard with iSCSI might have been specific to SANs offered by Dell, or perhaps resolved in updates with DPM 2010 or Windows Server 2008 R2, so your mileage may vary. If that's changed, I apologize. – Aaron Friel Feb 26 '11 at 1:12
Re: Andrew, if you've licenses to spare look at the comment below. For "Enterprise" CAL workloads (Exchange, SQL Server and Sharepoint) or for fine-grained temporal backups from servers, install agents on every VM. The overhead is substantially higher when backing up a VM versus backing up a local filesystem. Also note you can backup some workloads with very small intervals, like SQL Server can do transaction log backups to DPM every 15 minutes. Doing that at the VM level would be ridiculous. – Aaron Friel Feb 26 '11 at 1:14

The important thing to think about here is the kind of restores you want to perform.

If you want the ability to restore an entire VM (and I'm sure that you do, this is one of the key reasons why virtualization is so awesome after all), you should backup at the host level.

But there might be other kinds of restores you want to do that add flexibility. For instance, if you are running SQL server on one of the VMs and want the flexibility to only restore a single database from that VM, you would want to install an agent on the VM and do a SQL-based restore of the databases. Sure you could skip this and instead restore the entire VM, start it, copy the database off, etc but that's a lot of complexity for a simple database restore. Also, you might choose to only backup the VM once a week but backup the database every 4 hours. Of course, with this level of flexibility comes an increase in disk space usage. It's a tradeoff and only you can determine if it is worth it.

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