We have 4 ESX 3.5 servers, and I would like to increase the memory of the systems. All the servers currently have 8GB, can we add memory to one server without adding more to the rest, or do all of the servers in a cluster have to have equal memory?
You can have any amount of memory per server and any type of memory. You do not have to add memory on all servers if you do not want to.
I'm currently running ESX3.5 in the cluster with 1x24GB + 2x10GB RAM.
As anton pointe dout memory does not need to match in your esx hosts