Let’s start with a screenshot:

These are the properties of an HA cluster, as you can see there are two sections that changed:

1. “Enable Host Monitoring” is a brand new feature. Anyone who did network maintenance while HA was enabled knows why this feature will come in handy. Those that didn’t: Isolation response! If ESX is unable to send or receive it’s heartbeat and can’t ping it’s default isolation response address it will shutdown all VM’s. To avoid this behavior you can switch of HA for a specific host with this new feature. In just four words: Maintenance mode for HA.
2. Besides the amount of host failures a cluster can tolerate you can also specify a percentage. With the “host failures” option VMware uses the highest values of CPU and Memory reservations to calculate the amount of slots. (For more on slot / slot size read the Resource Management Guide for ESX 3.5) With the new option “Percentage of cluster resources” this isn’t the case. This new option uses the actual reservation of the VM and calculates the total percentage of resources used based on these calculations. If no reservation have been made it uses the default 256Mhz / 256MB reservation. In other words, you will be more flexible and will get a higher consolidation ratio. If the default reservation values are to low you can always use the advanced options to increase it. Another new option is “specify a failover host”. This option can be compared to “das.defaultfailoverhost”. The good thing about this option is that the designated host will be used for fail-over only. DRS will not migrate VM’s to this host, and it’s not possible to start VM’s on this host.