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Anyone know if it is possible to attach a virtual disk to a running hyper-V virtual machine so that it can be used for Windows Server Backup to use to backup the virtual machine and its system state to?

Edit: That is awkward then, I want to backup the virtualised system and data to a removable disk drive. Sounds like this is going to require a reboot every week when I want to swap the portable backup drive over.

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up vote 3 down vote accepted

Both of the other answers are incorrect - you can add attach a VHD to a running Hyper-V (2008 R2 or higher) VM provided you're attaching it to a virtual SCSI controller and not an IDE controller. If you want to make the entire removable drive available to the VM rather than create a VHD on it, you can also attach it as a pass-through disk if you offline it on the host first.

Once attached, you'll need to re-scan the disks from Disk Management.

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Thanks Chris, that works just fine. In fact with 2012 R2 I have found that once added and given a drive letter in disk manager it automatically comes back online with the correct drive letter. – NickC Apr 3 '14 at 16:57
Interesting! +1 for learning something new. It should be noted that this does NOT work in a clustered environment. Which mine is... hence the wrong answer below >.< – Byron C. Apr 4 '14 at 18:51

If you are talking about adding or attaching a second VHD(x) to an existing VM, the answer is yes, but only while the VM is powered off. You cannot perform ANY disk operations while the VM is running, this includes adding, compacting, expanding, merging or shrinking. You can only Inspect a disk on a running VM.

EDIT: You cannot add or change IDE disks, but as Chris said, you can work with a SCSI controller while the VM is running.

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