On 05/21/2012 05:02 AM, Paolo Bonzini wrote: > Eric, is it a problem for libvirt if a pause or target error during > mirroring causes the job to exit steady state? That means that after a > target error the offset can go back from 100% to <100%.
Libvirt would really like to have events present. If you emit an event on every change from <100% to 100%, and a counterpart event on every revert from 100% back to <100%, then that will help tremendously. For RHEL 6.3, libvirt requires 100% before attempting a drive-reopen. But since this proposal says qemu 1.2 won't even have a drive-reopen, but instead have a new block-job-complete, then libvirt should be okay if block-job-complete gracefully fails any time things are less than 100% (remember, drive-reopen has an attempted effect even if things are less than 100%, which is why libvirt had to pre-filter for that situation, but then again, RHEL never downgraded). In other words, I think downgrading out of steady state is not a problem, as long as events exist to help management track that, and as long as the command to pivot to the destination gracefully requires steady state. > > On the other hand, in other cases it can be desirable (qemu -S, run > streaming before the VM starts). Yes, libvirt would really like a way to be able to start a VM with mirroring active, in order to make it possible to support drive copy on persistent domains. -- Eric Blake ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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