**** 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
Also, you are now testing HA and not really DRS. DRS's performance is all about the algorithm/drs thread on the vCenter server and the amount of calculations required. For HA there is no technical reason indeed, for DRS there is...
CSI stands for "Cluster Services Infrastructure".
The "Fault Domain Manager" is a component (currently the only) of CSI.