You can optionally assign a shelf location to a stacked volume. When a stacked volume is resident in a VTS library, no shelf location is needed; however, if it is stored outside the VTS assigned to location SHELF you can assign a rack number using either the RACK or POOL operands. Specify RACK with a specific rack number or use POOL to allow DFSMSrmm to select the first empty rack number in that pool of shelf locations. During normal processing, DFSMSrmm storage location management processing assigns shelf locations to a stacked volume that must move to a shelf-managed storage location.