Thanks, that complicates the large-VM theory in a good way.
If these are long-established VMs that backed up fine for years, "too much free space on a new VM" probably isn't the whole story here.
Your deltas run from a completely different XO instance, on a different host, to different remotes, at non-overlapping times, so "deltas never fail, fulls do" might not be purely about job type, it could be tangled up with which instance or remote is doing the work.
If you ever get the chance to run a full from the XO instance that normally handles your deltas, that would help tell whether the timeout follows the job type or the instance.
I could easily be wrong, though, but that split feels worth isolating before we lean too hard on the free-space angle in https://github.com/vatesfr/xen-orchestra/issues/9181 .
MajorP93 created this issue in vatesfr/xen-orchestra
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Full backup fails on large VMs / VMs with lots of free disk space
#9181