Devices can be grouped together and defined as one group to the system. For instance, a group of 3590 tape drives in the same room can be grouped together and defined as 3590GRP. These device groups are known as esoteric unit names or esoterics. If you specify an esoteric on the SETOAM command for a group, you must ensure that this esoteric exists if an OAM tape has that esoteric specified in the UNITNAME field of the TAPEVOL table. Do not change the contents of that esoteric to introduce incompatible device types. Should the esoteric name be deleted or changed, the volumes that are associated with the esoteric name cannot be allocated. Because the TAPEUNITNAME cannot be resolved, the tape volume that is required for the request is not mounted and the allocation request fails.