@pierrebrunet I did try the "merge synchronously" option, but that didn't change anything. Can you expand on "your chains have an issue?" I understand the concept of chains, but in this particular case the situation is: Fresh install of XCP Brand new VM that has never been backed up before (though was built originally on another pool). There was no previously existing snapshot. New install of XO targeting a new NFS server with a ne backup job There shouldn't be any chain involved as literally everything is brand new. I cleaned up: Removed the snapshots from the VMs Unmounted the NFS Cleaned up the filesystem on NFS Remounted NFS Created a new backup job Left NFS with v4.2, enabled synchronous merge Restarted the job Same failure Some thing I noticed: When kicking off the job, the VHD appears in the NFS filesystem: /var/run/xo-server/mounts/d806298f-85cf-4565-bb7e-9fad479b941f/xo-vm-backups/e5f62657-8efb-3c2c-3397-2bfe01df5f0d/vdis/c82e4cd1-a0ee-4d7e-9e57-c77d8102593e# ls -alh 82c9959a-b4fa-46a1-a6ea-8cfbbeca864f/.1777916466905.20260504T174106Z.vhd In this example, this vhd file was 951mb. It remains there for about one minute, then disappeared. Shortly later the backup job fails, but I notice the snapshot remains, owned by control domain. That never seems to disappear. I think it's worth noting that I have imported several test VMs, as well as copied VMs cross-pool (from somewhere else to this pool) so it seems like the normal import/export mechanisms work properly. If you let me know what logs you'd like, I'm happy to upload them.

@florent Nothing has changed on the NFS (QNAP NAS) side; I had already been backing up to NFS before. It just stopped working over the weekend. What I did was commit changes to the master branch and update Ubuntu 24.04.

@john.c This is a good idea as well. If the previous suggestion of trying to do a DNS round robin approach doesn't work, this may be my best option. Thanks for taking the time to provide your suggestion!

@julienXOvates Got it. I didn't get a chance to work on this over the weekend, so sometime this week, I'll just bounce the host and see if it comes back. Right now, while I can SSH into it, the admin console appears to be frozen and unresponsive (over iLO).

@dkg Please also note that you should not use @jul1an ISO installer on production environment. Only on test env where you can afford to break things and lose data.

@stormi That is quite possible. I'll open a ticket for further investigation.

Hello @codemercenary In theory Xen is NUMA aware (See https://wiki.xenproject.org/wiki/Xen_on_NUMA_Machines) so you would leave memory interleaving option of the BIOS off so that Xen does what it thinks is necessary. But these kinds of settings are very very workload sensitive and in fact it's usually a good idea to just test what works best for you. Regards, Yann