A VMDK file can be grown while no virtual machine is using it. Growing the VMDK only makes the virtual harddrive bigger - filesystem within the VMDK must still to be grown with other methods.
On ESX Server:
vmkfstools -X
On ESX 3.5, you can also edit the VM settings and edit the harddrive when the VM is not running.
Note: On ESX the filename.vmdk file is just a file containing metainformation and "filename-flat.vmdk" is the actual data file.
However, vmkfstools operations are used on the metafile
On VMware Server Workstation and VMware Fusion:
vmware-vdiskmanager -x
If growing an existing vmdk file named "server1.vmdk" and it is to be grown so it's new size is 20GB, the command would be:
On ESX Server:
vmkfstools -X 20GB server1.vmdk
On ESX Server:
vmkfstools -X 20GB server1.vmdk
