CBT: the thread to centralize your feedback
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@FritzGerald 2 thing that i think could be causing, first check if u have set a dedicated nbd network on the pool.
Second u need to remove all snapshots from the vms and disable cbt on them. This will remove the cbt files and makes shure there will be a clean cbt chain.
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@rtjdamen Thanks a lot for the quick response. The second step I already tried. But I did not set up a dedicated nbd network yet. I will have to try that. Thanks!
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@rtjdamen
Thank you for your hint! I indeed did not enable NBD on my management interface. Somehow I did not notice that in the docs.Maybe it would be a helpful for others to mention in the docs that you need to enable NBD in: a.) the network settings b.) the vm disc settings and c.) the actual backup task in order to work.
Thank you again for your quick help!!!
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Not to dig up an old thread but was the issue with CBT being reset to 00000000-0000-0000-0000-000000000000 after a manual snapshot is taken with NFS storage ever confirmed or reproduced by Vates? I would love to start being able to use CBT and purge snapshots after each backup run, or have there been enough changes / improvements that this is worth testing again?
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@flakpyro i understand they did, but not shure if it is allready fixed or not. it had to do with the dedicated migration network being selected. maybe @olivierlambert is aware of the current status?
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@rtjdamen I do know the dedicated migration network was an issue. CBT data would be reset if you preformed a migration using a dedicated migration network, removing the dedicated network was a work around there. The next issue was taking a manual snapshot and removing would sometimes also reset CBT data. Perhaps i need to spin up a test VM and try again and i know there have been a lot of updates.
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Hi all,
We recently upgraded our production pools to the latest XCP-ng 8.3 release. After some struggles during the upgrade (mostly around the pool master), everything seems to be running fine now in general.
However, since upgrading, we’re seeing much longer durations for certain XAPI-related tasks, especially:
VDI.enable_cbt
VDI.destroy
VDI.list_changed_blocks (during backups)
In some cases, these tasks take up to 25 minutes to complete on specific VMs. Meanwhile, similar operations on other VMs are done in just a few minutes. The behavior is inconsistent but reproducible.
We’ve checked:
Storage performance is normal (LVM over local SSD)
No I/O bottlenecks on the hosts
No VM performance impact during these tasks
It seems to affect CBT-enabled VMs more strongly, but we’re only seeing this behavior since the upgrade to 8.3 — especially after upgrading the pool master.
Has anyone else seen this since upgrading?
Is there a known issue with CBT or coalesce interaction in 8.3?
Would love to hear if others experience this or have suggestions for tuning. -
I'm not aware of such issues (at least now)
(doesn't mean it doesn't exist more broadly but it's the first report). We'll upgrade our own production to 8.3 relatively soon, so it will be the opportunity to also check internally. -
@olivierlambert ok, maybe u experience some differences as well, we were on 8.3 since February and did patch last friday, since the patching is see a decrease.
What i believe is happening is that GC processes are blocking other storage operations. So only if a coalece is done on an sr i see multiple actions like destroy, enable cbt and change block calculations being processed. As far as i know this was not the case before, they also could take some longer but it was not related to (or i have never noticed it).
Maybe we can confirm if this behavior is by design or not?
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I'm not sure there's a change related to that but I can ask @Team-Storage
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Anyone else experiencing this issue?
https://github.com/vatesfr/xen-orchestra/issues/8713it's a long time bug that i believe is pretty easy to fix and get CBT backups to get more robust. Would be great if this can be implemented!
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Pinging @florent about this
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@olivierlambert yes the fix is in the pipeline (on xapi side )
it won't migrate a snapshot with cbt enabled, and won't allow to disable cbt on a snapshot -
Thanks!
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@florent so not an option solving this inside xoa? Could be usefull for the short term.
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Support found that automatic refresh of our sr every 30 seconds delayed this. It seems we had this for a longer time but now it’s more aggressive. Disabled this as this is not required. This resolves our issue here.
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Wow, rescan every 30sec? I thought the default value was 10 min or something
Do you remember setting it manually at some point? -
@olivierlambert No never changed it. From what i understand from Jon it's default this where his words "and all these SRs have auto-scan enabled. This means every 30 seconds, the pool master will scan the entirety of every SR". We changed this and the problem is gone.
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Okay, I thought the autoscan was only for like 10 minutes or so, but hey I'm not deep down in the stack anymore
