I had a customer ask about hot resizing (extend while VM is powered on) a VMDK for VM on a vVols datastore. They said they couldn't resize the disk and received an error. Turns out they had multi-writer enable on the disk. To clarify, you can hot extend a VMDK on vVols if the disk is not shared and using either multi-writer or physical bus sharing. These are typically used for WSFC or Oracle clustered applications and hot-extend is not supported.
Other caveats that can prevent you from resizing a disk; VM has an active snapshot, VM HW version, or another vSphere process or change is active. If you can't extend past 2TB, you may not have the supporting vSphere version.
Here are mode details on hot extend past 2TB:
Here's a quick video show how easy it is to hot extend a disk on a Windows 10 VM from 1TB to 2TB.
Hopefully this helps with hot-extend questions on vVols.