On Thu, 2021-06-24 at 12:32 +0000, Mariusz Karpiarz wrote:

Hi all, For live migration of volume-based instances (a Cinder volume used for the main OS disk) to work does the Cinder backend need to support multi-attach or at any point of the migration process are there multiple processes accessing the same volume? it does not need to support multi atach.

while the volume does need to be mapped to two host or qemu instaces for a period of time only one of the two instaces will ever be running. the other instace will be paused as libvirt is orcestrating the coping of the guest ram form the srouce to the dest. libvirt will pause the souce qemu instance before it unpauses the dest instance so the volume will only be acceessed by the source or dest at any one time but never both.