> In order to create a snapshot, I would have to read the whole VM through the slow NFS mount (i.e. 40 GB). This is the thing I want to avoid…
That can be worked around. - I also dont think that it takes that long. Creating a snapshot does not need to read through the whole vmdk when the VM is powered off. I dont think creating one takes longer than a few seconds.
If you know the exact nominal size of the VM a quick script can create a thinprovisioned vmdk of the same size and create a snapshot.
This snapshot can be easily attached to the vmdk on readonly vmfs.
You only need to edit the parentfilename hint.
If you backup the snapshot before you use it for the first time you can re-add the copy for later usage.