Hi all,
Just an update on our progress, i have been doing backups for around 10 larger vms now on CBT, i have seen this is working pretty well but it is not the wonderfull solution we had in mind.
First of all, the Alike backup software we now use to make CBT backups does have issues with multi disk vms, for some reason now and then the CBT got disabled by XEN on one of the disks resulting in a new baseline that needs to be created the next day, this is causing higher and longer backup times, still workable but it seems there are still issues with CBT in XCP-NG, i can determine if this is an issue of the alike software or that this is being caused by XCP-Ng itself. I have currently no other backup solution using the CBT so we canβt compare the results there.
Also a new issue can occur, when u create a CBT snapshot during peak hours it can cause issues with coalesce as well, the snapshot is deleted and it has to be coalesced into the base disk, but when the vm is under higher i/o load it can cause an endless process of coalesce. This is basically a limitation of the XEN garbarge collection process but it is giving issues with backups from now and then.
From what i understand XOA is working on CBT as well, i believe some fundamental changes are needed to get this all working in the same way as it currently is in vmware and other products. I think it would be much better and much more reliable if this kind of coalesces are done direct at the vm level and not limited to 1 task per SR (as i understand there currenlty is).
I am curious if anybody else allready is doing tests with this and does have some feedback that could help us on this problems.