Backups failing back to Full Backups
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So not sure why this problem has come back but all backups are failing back to Full backups.
2026-07-06T02_09_34.032Z - backup NG.txt <- this was a Planned full backup.
2026-07-07T02_00_00.007Z - backup NG.txt - first Delta backup after full fell back to full.
I just tried to disable "Purge snapshot data when using CBT" but still fell back to full. Unless i need to run a nother full job first?
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I think you've hit the known purge-snapshot-data issue. The XO incremental backup docs have a "Known issues" note (https://docs.xen-orchestra.com/xo5/incremental_backups#known-issues) about this: with purge snapshot data on, backups can transfer a full on every run, and the two suggested fixes are to disable purge (which you tried) or migrate the disk to another storage to reset the disk state.
Since disabling purge didn't clear it, the disk migration is probably the one that resets the CBT chain.
There's also an open issue matching your "it came back" symptom (https://github.com/vatesfr/xen-orchestra/issues/8713) where leftover invalid CBT snapshots keep forcing fulls until the chain is reset, so it's already tracked.
I could be wrong about which step actually clears it, so if migrating the disk fixes it for you, dropping a note on that issue would help the next person.
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