**** Disclaimer: 32 nodes is still the maximum supported configuration for vSphere 5 from VMware, this has not changed. This is purely a demonstration, use at your own risk ****
Recently while catching up on several episodes of the the weekly VMTN Community Podcast, an interesting comment was made by Tom Stephens (Sr. Technical Marketing for vSphere HA) in episode #150 regarding the size of a vSphere cluster. Tom mentioned that there was no "technical" reason a vSphere cluster could not scale beyond 32 nodes. I decided to find out for myself as this was something I had tried with vSphere 4.x and though the configuration of the cluster completed, only 32 hosts were property configured.
Here is a quick video on enabling the new HA (FDM) and DRS on a vSphere 5 cluster with 64 vESXi hosts, you should watch the entire video as it only took an astonishing 2minutes and 37seconds to complete! Hats off to the VMware HA/DRS engineering teams, you can really see the difference in the speed and performance of the new vSphere HA/DRS architecture in vSphere 5.
vSphere 5 - 64 Node Cluster from lamw on Vimeo.
BTW - If someone from VMware is watching this, what does CSI stand for? I believe this was the codename for what is now known as FDM