I was at a customer site and was showing him how to expand the VMFS datastore on vSphere 4. Problem was however, it would not increase. If you clicked on the "Increase" button in the VMFS datastore's properties, the next screen is supposed to show you the available "free" space left on that disk so you can use that free space to increase the VMFS size. However it was coming up blank.
I found a post that said to try and connect directly to an ESX/vSphere server and try the vmfs increase that way, as they were having the same problem. There are several posts from people (eg: http://communities.vmware.com/thread/220476?start=15&tstart=0)who that method worked for, even when it wouldn’t work when connecting to vCenter, like I experienced. So I had the customer try that method and it worked!
Here’s the other thread I found:
http://communities.vmware.com/thread/215584?start=15&tstart=0