>
> I am trying to do migration with two different block devices in the source
> and destination hosts. For example, in the source the data in /dev/vda
> are 'aaaaa'. The guest has a cache. These data are cached. In the other
> host, the data in this device are 'bbbbb'. If we do migration, I want
> the guest vm recognize this change. How does qemu deal with the cache
> data? Thanks.
If you want the guest to see different disk contents, then hotunplug the
original and hotplug in the new disk. Migration is NOT supposed to
change disk contents. Your problem is independent of migration.