It looks like this is identified and solved, I'll test on a new version of XO next week at some point, but I just wanted to confirm that I've been seeing what appears to be the same problem. This hasn't affected any of my full, delta or mirror backups, on any of the NFS targets - but it does affect two different Pool metadata & xo config backups. Both on different NFS targets on different schedules. It's an infrequent failure, sometimes not failing for a couple of days, but sometimes failing up to 3 or 4 times per day - this is on an hourly schedule. [image: 1787394387803-912ddd51-e6c1-4a62-8529-79d6b2fe8ad0-image.jpeg] My most recent failure on the hourly job was yesterday morning, the one before that was almost 24 hours earlier. This is currently on Xen Orchestra, commit 24913 but it was also noticeable on a version from the end of July. From what I've read, I'm guessing the fix will be in the main branch soon enough and an update will solve it, but if there's any useful information I can provide, please let me know.

That should be it, tks @poddingue

@pierrebrunet This week I only got 500 errors affecting 5 VMs. These 5 VMs were retried at VM-level and one fo these failed again (it failed to backup since I only have set 1 retry). I'm now looking into connection and bandwitdh to B2. I'm only reaching 200 Mbps to B2 with my current ISP so I'll tune concurrency so I reach those 200 Mbps with fewer VMs in parallel, making each single VM transfer faster. Concurrency was set to 8, I'll try with 3 VMs in parallel this weekend. Tks, Pedro

Anyone who is using Commvault to back up VMs please tell me what you are using for credintials since you have to connect directly to a pool? I am looking for a way to backup VMs using Commvault and us AD accounts or OIDC.

Thanks for the feedback.

Veeam scheduled a remote call with me and pulled more log files. Of coarse when we ran the backup job twice in a row both times al vms were successful. Veeam needs to baby sit our backups :). The call was cut short do to internet going down. I have uploaded the logs and waiting to hear back. Update - Veeam took alot more logs from Veeam and from xcp-ng pool. Their response back - I've got someone else getting similiar results, so I'm providing both of your logs to get some insights. Basically when you see the error, it's because something happened to the bitmap we left behind on the previous run and so next run, we re-read the entire disk. I've not found anything super clear to what's going wrong with the bitmap and why its gone, even from the Xen server logs, so I'm hoping from QA's eyes might see what I might be missing. I will keep you posted if they have any details.

XO 6.7.0 went out on 30 July, and the changelog carries Bastien's fix under Backups as "Fix failed status on successful retry", pointing at PR https://github.com/vatesfr/xen-orchestra/pull/10129 and back at this thread: https://xen-orchestra.com/blog/xen-orchestra-6-7/. Given what you said about keeping the backup XOA on a version you trust, I would not rush it, but that is the version to look for when you do move. I have not exercised the retry path myself, so if a retried VM still reports the job as failed after you upgrade, it is worth saying so here.

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?

This might have worked, at that time i've allready created new VMs from the information inside the Backup xml file. It worked out allright but building VMs this way, is quite tidious. Maybe there could be a way to find the correct installer and patches, to get a new host in a state to restore a pool backup, would be good.

@olivierlambert Happy to hear that they are providing results to be looked at. If there is anything else I can provide, please don't hesitate to ask. And I'll do my very best to be helpfull

A remote is not the same thing as a SR. For a remote, it's simple: disconnect it (click on "Enabled" so it's disabled then), do whatever you need on the NFS server, re-enable.

I think this is fixed in 6.7: when a delta backup falls back to a full, the task now shows the actual reason instead of just contradicting itself the way you and Andrew both saw (PR #10148). Worth checking after you upgrade.

Both things reported here look fixed in 6.7: the retry succeeding but the job still showing as failed (PR #10129), and the EEXIST: file already exists error, which happened when a job got recreated after a crash (PR #10139). Curious if upgrading clears it for you all too.

The progress bar issue you and Florent were chasing looks fixed in 6.7 (PR #10133). Worth upgrading and seeing if it moves now instead of sitting still. Separately, since this thread is specifically about QCOW2 backups: 6.7 also fixes an offset bug that could leave incremental backups mostly empty after the first block when NBD isn't enabled. Worth a look at the release notes if that's your setup too.

Good news that it sorted itself out. Both changes went in at once and the next run came back clean on the ADDS VMs too, so I don't think there's anything left to pin down here, and I'd rather say that than invent an explanation after the fact. Your question about the snapshot modes was the useful thing to come out of this thread. I went looking, they genuinely aren't documented anywhere, and that's written up on our side now If the fall back to a full ever comes back on the ADDS VMs specifically, that would deserve its own thread with the SMlog output @tjkreidl asked for, since nobody got to look at that part.

Thanks for the feedback @norpan , worth it! Ping @florent