[libvirt] Live Migration with non-shared storage for kvm
Daniel P. Berrange
berrange at redhat.com
Tue Jan 26 10:14:47 UTC 2010
On Tue, Jan 26, 2010 at 11:57:25AM +0200, Kenneth Nagin wrote:
>
> On January 5 I asked for comments on adding libvirt support for live
> migration with non-shared storage on kvm. I did not get any comments so I
> am repeating my request:
Sorry I missed your original mail - January 5th was unlucky timing, since I had
a backlog of several thousand emails from the xmas break :-)
> Support for live migration between hosts that do not share storage was
> added to qemu-kvm release 0.12.1.
> It supports two flags:
> -b migration without shared storage with full disk copy
> -i migration without shared storage with incremental copy (same base image
> shared between source and destination).
Interesting, I'd not seen those flags before. How does that work with the
destination side, if the disks do not already exist there ? Does the
mgmt app have to just create a zero-sized disk, start QEMU & then let the
data be copied. I'm guessing QEMU can't create the disk itself, since it'll
be trying to open it on the destination before the incoming migration even
starts.
> I suggest adding these flags to virDomainMigrate.
That sounds reasonable.
> If I'm not mistaken qemuMonitorTextMigrate is the function that actually
> invokes the kvm monitor.
> Thus, it would be necessary to pass the flags to qemuMonitorTextMigrate..
> But qemuMonitorTextMigrate does not have a flag input parameter. I think
> the least disruptive way to support the new flags is use the existing
> "background" parameter
> to pass the flags. Of course this would require some changes to the
> upstream functions that are invoked for migration.
That is an internal function, so adding extra parameters to it is no
problem at all - no need to reuse/abuse existing parameters.
Daniel
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