In my recent post about the new large 64TB VMDKs available in vSphere 5.5, I mentioned that one could not hot-extend a VMDK (i.e. grow the VMDK while the VM is powered on) to the new larger size due to some Guest OS partition formats not being able to handle this change on-the-fly. The question was whether hot-extend was possible if the VMDK was already 2TB or more in size. I didn’t know the answer, so I decided to try a few tests on my environment.In my experiment I added a 3TB disk to my VM, then I tried to grow it to 4TB while the VM was still running. Note that there is no problem with adding disks while the VM is running; we are talking about growing a disk online. Unfortunately this did not succeed either:
Therefore, you cannot grow VMDKs which are less that 2TB to greater than 2TB on-the-fly with vSphere 5.5, nor can you grow VMDKs which are already > 2TB to a larger size on-the-fly. The growing of a VMDK in vSphere 5.5 to a size above 2TB can only be done when the VM is powered off.