Hyper-V Checkpoints - exclude certain disks (VHDX)

Question

Hi,

Is this possible? I know in most cases it wouldn't be a good idea but consider this scenario:

C: drive = 200GB
D: drive = 200GB
E: drive = 200GB
F: drive = 200GB
G: drive = 2TB

We're using CSVs via a SAN.

C: drive VHDX is on a LUN that is shared with other OS C: drive (LUN is 1TB)
D: E: F: drive VHDX are shared on another LUN (LUN is 1TB)
G: drive VHDX is on its own dedicated LUN (LUN is 2.01TB to be able to exactly fit a 2TB VHDX)

All are fixed size, not dynamically expanding.

We're copying data from the old server to this new one. The G: drive is a typical folder/file layout (nothing fancy like SQL DBs for example) and the source data set is about 500GB.

Now part way through data copy (robocopy) a checkpoint is taken of the VM. This creates an AVHDX file and new writes go there. Now because the VHDX by itself fills up the LUN/CSV, the AVHDX basically has no space to grow so causes the Hyper-V worker to pause the entire VM.

Even once the data copy is complete and the new server is in production, a snapshot would cause the same effect, although new writes day-to-day will be a lot less than the initial data copy. I'm thinking here of the monthly patching process; to protect the VM in case of a buggy or failed update, I wouldn't necessarily care about protecting any drives that aren't hosting the OS.

Don't say the obvious by increasing the 2TB LUN to be 3TB or something. We don't have capacity on the SAN for that luxury.

Thanks

Answer 1

There is no way to exclude .vhdx in checkpoint as its by design.

However , you can changed .vhdx from fixed to dynamic

Answer 2

Hi @Lanky Doodle

If you were to exclude a VHD from the snapshot, and then you applied the snapshot, the file system on the VHD would immediately be corrupted because the in-memory file system state would assume that the virtual disk was in the same state as the moment the snapshot was taken. It would flush out pending writes, which would then be written to the VHD.

If you really want a file system that doesn't come along with the snapshot, one which will be coherent when the snapshot is applied, you need to make that file system external to the VM itself, or you need to make it read-only

Hope this resolves your Query!!

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