Re: [Qemu-devel] Storage requirements for live migration

[Kevin Wolf]

Am 11.11.2011 10:55, schrieb Daniel P. Berrange:
> On Fri, Nov 11, 2011 at 10:38:20AM +0100, Kevin Wolf wrote:
>> Am 11.11.2011 01:11, schrieb Anthony Liguori:
>>> I did a brain dump of my understanding of the various storage requirements 
>>> for 
>>> live migration.  I think it's accurate but I may have misunderstand some 
>>> details 
>>> so I would appreciate review.
>>>
>>> I think given sections (1) and (2), the only viable thing is to require 
>>> cache=none unless we get new interfaces to flush caches.
>>
>> Yes, I think we should strongly recommend cache=none/directsync, but not
>> enforce it. As you said, for clustered filesystems other options should
>> work, so we should allow users to choose to make use of that.
> 
> WRT libvirt, we have a concept of 'tainting' for guests. We set taint
> flags whenever the management application requests a config, or performs
> an action that we know to be potentially dangerous. These end up as log
> messages in the per-guest logfile, so when users report bugs we can see
> from the log that something "bad" has been done to the guest.
> 
> At the very least, it sounds like we should make libvirt mark guests as
> tainted, if they have been migrated with cache != none, so this is easily
> identifiable by BZ support people.
> 
> We might also want to make a libvirt host level config option to allow
> host admins forbid migration without cache=none.

Yes, I think this would be a good approach.

Kevin