Selects which disk to act on, matched by any of:

• vSphere device label, e.g. "Hard disk 1";
• disk file base name, e.g. "kube15_1", taken from a backing file named "[datastore1] kube15/kube15_1.vmdk";
• controller moniker matching how vSphere itself displays the disk's address, e.g. "SCSI(0:2)" or "IDE(1:0)" (controller bus number : unit number).

Cannot be combined with Device Number.

• Add: optional; if given, the new disk's file is named after it instead of the default "<vm>_<N>" scheme (fails if a disk with that name already exists).
• Edit: selects the disk to resize; may be left blank if the VM has only one disk.
• Remove: always required (unless Device Number is used), since removing the wrong disk deletes its data.