i switched one of the backups for my extra pool from nfs to smb and its been sitting so i expect it to fail. might be a smb issue. ill update this post with results once it either fails or works [image: 1785952420501-2d4d9b1d-9aa5-4f1d-a1c1-d8ea5e079047-image.jpeg] i did test smb and it works. back to nfs works [image: 1785952526594-b2b807b8-d422-4719-8088-817b08d3c5ad-image.jpeg]

What kind of storage are you using? Is it a 4K block native storage? You should be able to see if you can create a virtual disk easily with xe vdi-create name-label=test virtual-size=1G sr-uuid=356475ac-…

@msupport said: The CBT metadata VDIs remain as snapshots, but their VHD parent references point to nothing. The tapdisk crashes, the VM loses disk access, the filesystem becomes corrupt. For VM-A (SQL Server), both disks (60GB + 80GB) have broken CBT snapshots. virtual-size=0, physical-utilisation=0. For VM-B (File Server), the 80GB disk has a broken CBT snapshot. Interestingly: virtual-size=85899345920 (80GB, same as the base disk) and physical-utilisation=8388608 (8MB). This is different behavior from VM-A — possibly a different code path in the CBT lifecycle. In my testing i did see similar issue Edit - updated with actual error message from what I am getting. The first full backup were all successful. This first delta backup have 4 vms with this error. The first time I saw similar was only 2 vms. 8/5/2026 5:34:50 PM Warning : Failed to use CBT: [Task e75c4247-2ee1-7b51-088c-b970ace60f3d (Async.VDI.list_changed_blocks) failed: . SR_BACKEND_FAILURE_460. . Failed to calculate changed blocks for given VDIs. [opterr=Source and target VDI are unrelated] For me i took it as because i original had backups from veeam 12.x the first xcp-ng beta. Pointed new backups from 13.1 to older backups. I then purged all older backups and started with a fresh backup chain. I ended up reverting to the windows base as i was not able to get the windows mount server setup. This was setting up from a windows client using the console to setup the repo.

Hi, I found your original request. I will make sure someone from the Sales team responds ASAP. Regards, Dan

So I ended up going with the Windows B&R as i could net setup the windows mount server when setting up the repo for the backups. It would setup the linux one but not the windows one. This was with using the veeam console from a windows client. So i ended up with the Windows one. Now after a few backups i am see this warning / error.... 8/5/2026 5:34:50 PM Warning : Failed to use CBT: [Task e75c4247-2ee1-7b51-088c-b970ace60f3d (Async.VDI.list_changed_blocks) failed: . SR_BACKEND_FAILURE_460. . Failed to calculate changed blocks for given VDIs. [opterr=Source and target VDI are unrelated] First i thought it was because i maped the new job to older backups from Beta v1. So i purged all old backups and started fresh. The full backups were successful. Now on first delta 4 out of 7 vms have that warrning. This a Veeam issue or xcp-ng?