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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 assyoma it - info assyoma it
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