Do you run into situations where you want to limit the eligible devices for a certain set of jobs or applications?  With APAR OA59161 (z/OS V2R3 and above), you are now able to do that through SMS policy management with enhancements to the existing SMSHONOR support.  The initial SMSHONOR support was provided in z/OS V1R11 through specification of the SMSHONOR keyword on the UNIT parameter of the DD statement.  When SMSHONOR is specified, MVS allocation will use what is specified on the UNIT parameter as long as there is an intersection between what SMStape considers eligible and what is specified on the UNIT parameter.  This initial support was referred to as “Demand Allocation with System-Managed Tape”.   Prior to that support, SMStape would always ignore what was specified on the UNIT parameter and would instead allocate using the assigned SMS constructs.  There was no easy way to limit the devices that SMStape considered eligible or to select a particular device.  With RFE 127904, clients also wanted the ability to select what devices could be used through SMS constructs (policies).  With APAR OA59161, SMSHONOR can also be enabled through the SMS tape storage group construct.  This broadens the original SMSHONOR support and makes it easier for clients (through SMS policies) to reserve a set of devices for critical applications by limiting the devices used by their less critical applications.   For more information refer to Demand Allocation with System-Managed Tape in the z/OS DFSMS Object Access Method Planning, Installation, and Storage Administration Guide for Tape libraries and APAR OA59161.