Hyper-V Backup Limitation – backing up pass-through disks

Hi all,

We’ve been asked a few questions about pass-through disks.

At the moment, our Hyper-V backup solution only works when the Guest HDDs are VHD files, not physical volumes. (A pass-through disk is where the disk is connected to the host, marked as “offline” on the host, and passed through to the Guest where it is “online”.)

This is a limitation in the Microsoft Hyper-V VSS Writer, and also our Hyper-V Granular Restore Console only works on VHD guest HDDs as well.

The good news is that there’s no compelling reason to use pass-through disks anyway, so this limitation is almost a moot point. There is very little performance difference between a Fixed size VHD virtual disk and a physical volume, as explained in the MS blog: Working around the pass through limitations of the hyper-v vss writer.aspx

Happy Hyper-V Backups!

1 thought on “Hyper-V Backup Limitation – backing up pass-through disks”

  1. I was told that to take a snap shot in Hyper-V with pass-through disk I can disconnect the pass-through disk, take the snap shot and reconnect the pass-through disk. Is that correct? If it is, how safe is it and how do i go through the process of disconnecting and then reconnecting the disk? Thanks for your help.


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