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.

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?

Pour l'ISO montée deux fois : My bad, j'ai ajouter un truc en trop sur mon précédent fix. Une PR est en cours pour corriger ça. Pour le problème principal : J'ai identifié la cause, mais je n'ai pas encore de solution. Sans les drivers Xen (non initialisés avant l'installation), une VM est limitée à 4 périphériques. La séquence de boot ne peut donc pas détecter le second disque contenant le fichier Kickstart (ks). Côté Packer, on semble être bloqués par cette contrainte XCP-ng. Les seules alternatives actuelles seraient de se limiter à : 2 disques + 2 CD ou 3 disques + 1 CD + HTTP (Note : L'installation manuelle fonctionne car l'installateur démarre directement, avec le driver xen_blkfront, alors qu'avec Packer, l'injection de notre fichier interrompt le flux de démarrage classique). Je vais fouiller encore un peu, mais sans certitude d'un contournement possible. (et je regarde pour ajouter le CDlabel)

@dinhngtu Just wanted to pass along some feedback from trialing the newest version (9.2.350) -- in case it's helpful. When comparing to the previous version (9.1.200 -- and earlier versions as well) on Windows 11 Pro VM (with latest updates), this new version results in noticeably slower VM restart and shutdown times (at least when monitored via xenadmin [on Windows] and xenadminqt [on Linux]).

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.

@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

Excellent! It's really cool to see how XO Backup and Replication can help you to migrate easily

@anthoineb, We checked both SMlog and xensource.log for the two latest incidents on hypervisor 172.30.50.181. There was no VM or storage pause/unpause operation before either stall. The only matching pause/unpause pairs were part of our later forced VM.hard_reboot: 2026-08-19, VM 172.30.52.185: stall confirmed around 20:24; pause at 20:36:37 and unpause at 20:38:12. 2026-08-20, VM 172.30.52.182: stall confirmed around 20:24; pause at 20:30:07 and unpause at 20:31:26. The first related VDI operations in SMlog were also the vdi_deactivate actions initiated by those reboots. Therefore, we do not see a pause/unpause immediately before or at the onset of either lock.

@poddingue said: What I can't tell you is what set that particular combination on your VM in the first place. Does it ring a bell? I have no Idea. I had it on "Protect from accidental shutdown" but turned that off again, later. Doing this again (on, off) helped, as you said. Thank you so much!

@acebmxer Thank you for your quick feedback.

@poddingue Thanks for running the -31 numbers — good to have it confirmed that the ttyS0 removal stays worth ~3-4s even with the clock fixed. Agreed on not rushing -proposed to production; we'll pick up -31 when it promotes and keep the cloud-init tweak permanently.

@poddingue Thank you for the analysis. I'd give you a rep if I could

@andriy.sultanov @andriy.sultanov said: @pandusen As Teddy said above, you can't passthrough a PCI bridge, so there's no PCI devices xapi shouldn't omit here. I am not trying to pass through the bridge only the end points. The Intel arc's have 2 end points: The GPU and the Sound device. "xe pci-list" only reveals the GPU, not the sound device. (this works for nvidia and AMD) But "going the xen-cmdline way" shouldn't break anything, that's what xe pci-disable-dom0-access does behind the scenes. What issues did you see? Which steps did you follow? the sound device is available in the lspci list and can be passed through using CLI. But doing so, (using CLI for passtrough) undoes everything done using xe or the passthrough gui in XO. and results in this: https://xcp-ng.org/forum/topic/10609/xcp-ng-8.3-pci-passthrough-issue so yes, its does break something.

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.

@poddingue Fistst of all I appreciate your answer and your position. The thing is that, even though the proxy code itself is opensource, the functionality of the plugin is basicaly behind a paywall. We are not talking about support. Actual functioning of the plugin after compiling from sources depends on license availability and there is no option to select no support or something along the lines "I built it myself from sources". Without patching the code even though the proxy is otherwise functional the backups won't work because of missing license. Hopefully the powers that can will provide an acceptable albeit community supported way to use the proxy cleanly, without touching license checks. Best regards!

Thanks for actually booting one, that's the bit I skipped. -84s versus -10s without console=ttyS0 matches the Ubuntu ratio, and it's the first EL10 number anyone has measured rather than read from the source. That settles the question I left open. A real-world measurement is vastly better than a source-code read, right? Thanks for the backport request, too. Since CentOS Stream sits upstream of RHEL and Rocky, if the backport lands there, it should be the earliest signal that the rest of the family will follow.

I put both of your questions on a spare host, because I couldn't answer either from memory. On colons: xe creates a key literally called auto_poweron:true with an empty value, so the entries you saw were three separate keys and none was the real auto_poweron, and typing false afterwards just made another one. It exits 0 and prints nothing every time, which I'd call a rough edge rather than a feature, though other-config is free-form by design so I don't know that the CLI is meant to validate keys at all. On the sleep: with rc.local executable and no sleep, it fired at 16 seconds of uptime and xe appliance-start came back with Error: Connection refused (calling connect ), exit 1, in under a tenth of a second. The VM stayed halted and nothing was reported anywhere, since rc.local has no terminal to print to. rc-local.service only orders after basic.target and network.target, nothing toolstack-related, while xapi-wait-init-complete.service took 30 seconds on that host, which is presumably why 60 was barely enough for you. There's an xapi-init-complete.target that looks like the right thing to order a unit against instead of guessing at a delay, though I haven't tried it so treat that as a lead rather than advice. The executable-bit half is in the docs now, it went onto the troubleshooting page after you reported it: https://docs.xcp-ng.org/troubleshooting/common-problems