This is an external key value used to correlate this deletion task with the corresponding DVS object as vCenter itself identifies it. Because UCS Manager and vCenter each have their own internal identifiers for the same DVS, this extKey on the task is what lets UCS Manager tell vCenter exactly which DVS object to delete, rather than relying on name matching alone. If this deletion task never completes and extKey doesn't match any DVS currently visible in vCenter, that mismatch itself explains the failure; the DVS may have already been manually removed from the vCenter side.