On 06/24/2014 06:08 PM, Xiongzi Ge wrote: > Hi Eric, [we tend to avoid top-posting on technical lists]
> > This really works if I set up the same configuration (/dev/vda in the > guest) but the physical block devices are not the same after migration.The > ABI is the same. When the guest cache stores a page like 'aaa' which is in > the block device of Host A. If the cache in the guest is also migrated to > Host B, but data in the block device actually are "bbb" in Host B now. The ABI is NOT the same if the two host files do not have identical contents; it's just that qemu cannot diagnose your bug. > What > will happen? Will the cache data in the guest be migrated to the other > host? The vmstate function in the qemu seems doing something to save the > vm state and the device state. > Who knows what happen? You're in undefined territory, because you violated the premise that migration does not change disk contents behind the guest's back. > Should the guest re-open the block device and delete the previous cache > data or just check the consistency of the cache and the block device? Rather than trying to figure out what happens with undefined behavior, how about you hot-unplug the old host device, then migrate, then hot-plug the new host device. That way, the guest will KNOW it it is connecting to a second disk, and not be confused by anything it cached about the first. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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