A few minutes ago I took a quick look at the summary tab of my cluster. In the VMware HA box I noticed the following line: “Current Failover Capacity: 0 hosts”…
After opening the “HA Advanced Runtime Info” link it turns out I had only 80 HA Slots in my cluster (256 MHz, 2 vCPU’s and 2048MB RAM). After some research I detected 1 VM with a memory reservation (2048MB), after I removed the reservation the available slots jumped from 80 to 329 🙂
The HA box now say “Current Failover Capacity: 4 hosts”. Just another example why you don’t want to use reservations in a vSphere cluster.
For more details and technical background regarding VMware HA I suggest reading the “HA Deepdive” article written by Duncan Epping @ yellow-bricks.com: http://www.yellow-bricks.com/vmware-high-availability-deepdiv/