Assigned memory is not considered by HA in terms of failover capacity, but reserved memory is. By default, the memory reserved for a VM is 0MB, each VM does have a memory overhead though which counts as reserved memory. Also, while failing over , it will check the VM for any reservation and Memory overhead .
HA has been redesigned in Vsphere 5 . it now uses a new mechanism called the Master/Slave node concept. This concept is fairly straight forward. One of the nodes in your cluster becomes the Master and the rest become Slaves. I guess some of
> restarting failed virtual machines
> exchanging state with vCenter
> monitor the state of slaves
As mentioned when a master fails a election process is initiated. The HA master election takes roughly 15 seconds. The election process is simple but robust. The host that is participating in the election with the greatest number of connected datastores will be elected master. If two or more hosts have the same number of datastores connected, the one with the highest Managed Object Id will be chosen. This however is done lexically; meaning that 99 beats 100 as 9 is larger than 1
wintual 