Re: Ceph and KVM live migration

[Vladimir Bashkirtsev <vladimir@bashkirtsev.com>]

On 01/07/12 10:47, Josh Durgin wrote:
> On 06/30/2012 05:42 PM, Vladimir Bashkirtsev wrote:
>> Dear all,
>>
>> Currently I testing KVMs running on ceph and particularly testing recent
>> cache feature. Performance is of course vastly improved but still have
>> occasional KVM hold ups - not sure who is at blame ceph of KVM. But I
>> will deal with it later. Right now I've got myself a question which I
>> could not get answered myself: if I do live migration of KVM while there
>> some uncommitted data in ceph cache will this cache be committed prior
>> cut-over to another host? Reading through the list I've got an
>> impression that it may be left uncommitted and thus it may cause data
>> corruption. I just would like a simple confirmation if code which
>> commits cache on cut-over to new host does exist and no data corruption
>> due to RBD cache+live migration should happen.
>>
>> Regards,
>> Vladimir
>
> QEMU does a flush on all the disks when it stops the guest on the
> original host, so there will be no uncommitted data in the cache.
>
> Josh
Thank you for quick and precise answer. Now when I actually attempted to 
live migrate ceph based VM I get:

Unable to migrate guest: Invalid relative path 
'rbd/mail.logics.net.au:rbd_cache=true': Invalid argument

I guess KVM does not like having :rbd_cache=true (migration works 
without it). I know that it is most likely KVM problem but still decided 
to ask here in case if you know about it. Any ideas how to fix it?

Regards,
Vladimir