Bruce, No the minidisk is a logdisk of a fileserver. It uses a CMS RESERVE to allocate all the space. The DASD on which the minidisk resides it is full y controles by Dirmaint (EXTENT CONTROL). I think it is meant CMS RESERVE command.
Dirmaint manual for CMDISK states: The disk must be formatted as a CMS disk and must not be RECOMPed or RESE RVEd. Best regards, Florian Bilek