The Update-VmfsDatastore cmdlet requires you to have a VMFS5 datastore as the temporary datastore. This is a problem if you want to do an in-place upgrade of your datastores. Because, how do you upgrade the final VMFS5 datastore to VMFS6, if there are no VMFS5 datastores left to use as a temporary datastore? If the VMFS5 datastore to be upgraded is in maintenance mode, there are no virtual machines to be moved and it should not be necessary to specify a temporary datastore. Going to the storage team and request a temporary extra datastore just for the upgrade, should not be necessary if you have enough free space on your datastores to do the upgrade in-place. It would be great if the Update-VmfsDatastore accepts both VMFS5 and VMFS6 datastores as the temporary datastore.