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

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 07.02.2014 18:46, Orit Wasserman wrote:
> 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.

So there is no any kind of sync in QEMU after migration finished,
correct? Looks too mucn to enforce "sync" option for NFS as we really
need it for once.


-- 
With best regards

Alexey Kardashevskiy -- icq: 52150396