I think you'll need to migrate to vsphere first:new version allows VMFS hot extensions.
In VI3, you need to create a new LUN instead of increasing the size of the existing one. 2 options:
- Big LUN (with total needed space),cold migrate or storage vmotion all VMs & free up previous LUN.Recommended.
- New LUN with desired new space,and configure it as an extension of previous LUN (same VMFS across 2 LUNs).Not recommended.