Hello @olivierlambert,
After upgrading to commit 05c4e, I cannot reproduce this issue again. It seems to work much better.
Thanks

@olivierlambert Xen Orchestra, commit 804af
Both SRs are the shared storage by Fibre Channels connection (multipathing enabled). I tested on the Windows or Linux guest system as well. XenTools respectively 9.4.0/9.3.3 and 8.4.0-1 respectively.

Hi,
I observed one issue with the backup process when the CBT is enabled. The case is showing when the VM has two disks on different SRs. When the backup tries to be taken, it fails, and the machine goes to a state where no other changes/reconfiguration is possible. It is not possible to disable CBT, move a disk to a different SR or create another backup. Sometimes after a failed backup the console access and machine are freezing. Everything works fine when all of the VM disks are on one SR.

The logs from the first backup: