[CentOS] About Memory mirroring

Greetings,

Was wondering if any software exists for mirroring memory across hosts like what drbd does for disks.

I am somewhat aware of copying of a VM's memory when a live migration is done.

Another query, as I have not seen too many VM migrations, is that what happens to the memory contents such as data yet to be written onto disk, states etc happens when one of the RHCS cluster hosts which is running VM fail: does the cluster restart the machine?

An example perhaps would be suppose the VM is running a movie what would the user's experience would be.

I tried it on cluster with ctdb. The movie simply restarted.

Any experiences?