NFS and unsafe migration

Hi all, I have a question about NFS datastore and unsafe migration. When migrating a virtual machine having a virtio disk in writeback cache between two hosts sharing a single NFS datastore, I get the following error: "Unsafe migration: Migration may lead to data corruption if disks use cache != none or cache != directsync" I understand why libvirt alerts for unsafe migration in cases where no coherency is enfoced by the underlying system; however, is it really the case for nfs? From what I know (and from the man page), by default nfs has open-to-close consistency, which seems quite right for migrating a virtual machine between (as only one host at a time reads/writes/locks the virtual disk files). I know that I can simply use cache=none to let the problem go away; however, this significantly impairs performance when used on nfs. Am I missing something? Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti(a)assyoma.it - info(a)assyoma.it GPG public key ID: FF5F32A8