Re: [Qemu-devel] migration question: disk images on nfs server

[Orit Wasserman <owasserm@redhat.com>]

On 02/07/2014 06:35 AM, Alexey Kardashevskiy wrote:
> Hi!
>
> I have yet another problem with migration. Or NFS.
>
> There is one NFS server and 2 test POWER8 machines. There is a shared NFS
> folder on the server, mounted to both test hosts. There is an qcow2 image
> (abc.qcow2) in that shared folder.
>
> We start a guest with this abc.qcow2 on the test machine #1. And start
> another guest on the test machine #2 with "-incoming ..." and same abc.qcow2.
>
> Now we start migration. In most cases it goes fine. But if we put some load
> on machine #1, the destination guest sometime crashes.
>
> I blame out-of-sync NFS on the test machines. I looked a bit further in
> QEMU and could not find a spot where it would fflush(abc.qcow2) or close it
> or do any other sync so it is up to the host NFS mountpoint to decide when
> to sync and it definitely does not get a clue when to do this.
>
> I do not really understand why the abc.qcow2 image is still open, should
> not it be closed after migration succeeded?
>
> What do I miss here? Should we switch from NFS to GlusterFS (is it always
> syncronized)? Or if we want NFS, should we just boot our guests with
> "root=/dev/nfs ip=dhcp nfsroot=..." and avoid using disk images in network
> disks? Thanks!
>

For NFS you need to use the sync mount option to force the NFS client to sync to
server on writes.

Orit
>
>