Comment:
The problem is due to a configuration problem in the NFSv4 server and/or clients. Probably related to the NFSv4 ID <-> Name Mapping (idmap).
Thus, this is not an I/O-related problem.
The solution/requirement is to make sure that the libvirt-qemu user has the same UID/GID on all systems that it might be migrated too.
Comment:
The problem is due to a configuration problem in the NFSv4 server and/or clients.
Probably related to the NFSv4 ID <-> Name Mapping (idmap).
Thus, this is not an I/O-related problem.
The solution/ requirement is to make sure that the libvirt-qemu user has the same UID/GID on all systems that it might be migrated too.