@archw can you try to restore the full VM and see if the files are here ?
what is the file system on the windows VM ? is it possible that there are special permission/protection that block the files to be listed ?
a little more tricky, but we provides to to mount the backup on a linux server with the command line tool here : https://github.com/vatesfr/xen-orchestra/tree/master/%40vates/fuse-vhd
Different use cases: Ceph is better with more hosts (at least 6 or 7 minimum) while XOSTOR is better between 3 to 7/8.
We might have better Ceph support in the future for large clusters.