CBT disabling itself / bug ?

[Pilow]

Hi,

Latest XOA, with fully patched XCP 8.3 here.

I'm fiddling around again with NBD+CBT in backup jobs (was avoiding CBT for a time, to reliably control my backups and avoid unnecessary KEY points) in the context of THICK SRs to spare some space.

I know that CBT is reset when migrating from one SR to another.

But here is what I encounter :

• VM has no CBT enabled on its VDIs, it is on a SHARED SR in a pool of 3 hosts
• backup option changed for NBD+CBT, was only NBD before
• CBT is enabled on the next run by the backup job, I get a delta (was expecting a FULL ?)
• next run, delta, as expected
• i migrate this VM on another HOST, without changing its SR
• CBT is immediatly disabled ? why ??
• next run of backup it tries a delta, but "fall back to a full" (normal as CBT has been disabled...), and do a KEY point on the remote
• next run is a delta as expected

does this mean if I do a rolling pool update or host maintenance that will move the all VMs around, all CBT will be disabled and I should expect a FALL BACK TO FULL on all my NBD+CBT enabled backup jobs ??!

why disabling CBT on a change of HOST and no move of SR ?

[flakpyro]

@Pilow Sounds very similar to my experiences with CBT.

Check out my post here (and keep reading from that point down)
https://xcp-ng.org/forum/post/88968

Can you check with the same commands i used?

[Pilow]

@flakpyro indeed seems related.

I also have this bug :

on some VMs all jobs do KEY points, but in the backup logs they are indeed DELTA

you can see as mere Megabytes are transfered that it's a delta backup... but point is presented as KEY

here is the log :

[Pilow]

about these KEY backups, I think perhaps LTR got in the way @florent @bastien-nollet

still no way of knowing WHEN a weekly/monthly backup is happening ?

[florent]

@Pilow I will take a look in deep later, but the key/delta and disk usage is set during backup, even if they are merged during LTR retention