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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

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!



-- 
Alexey