VMware is a great virtualization solution but since the first version the High Availability feature had a weakness that I never liked.
A vSphere 4.x cluster for example use a primary/secondary node architecture: the first 5 hosts that join the VMware HA cluster are automatically selected as primary nodes. All the others are automatically selected as secondary nodes.
That means that no matter how many nodes your cluster has, if all the 5 primary nodes are down, your entire virtualization environment is unusable.
Microsoft Hyper-V doesn’t have this limitation because uses a classic Windows Clustering feature that uses node and disk majority.
Now with vSphere 5.x the HA feature has changed to avoid this behaviour.
The concept of master and slave still exist but it’s dynamically assigned so if the master fall down, a new master role will be assigned to a slave.
This great article can explain in depth the changes made to the vShpere 5.x architecture.