Well, that's not quite true. You can expand the disk. That's not the problem. You can do that using the command 'vmkfstools -x' as described here:
VMware KB: Adding space to an ESXi/ESX host virtual disk
The problem is that by using disk utility it is currently not possible to expand the size of the partition:
VMware KB: Unable to extend a partition using the guest Disk Utility after extending disk of a virtual machine running Mac OS X
So, what's the solution?
Well, it's actually quite simple:
- Create a new Hard disk of the size you need.
- Restore the contents of the too small disk to the new disk using disk utility.
- Detach both disks from the virtual machine
- Rename the old disk by issuing the command 'vmkfstools -E OldNameas shown here VMware KB: Renaming a virtual machine disk (VMDK) via the vSphere Management Assistant (vMA) or vSphere CLI (vCLI)
- Rename the new disk by issuing the command 'vmkfstools -E NewName.vmdk OldName
- Attach the new disk to the VM
- If everything is working, delete the old disk