In addition to an object being stored inside a library (library-resident), an object can be assigned to a "shelf" (shelf-resident) location within the storage hierarchy. The following concepts apply to shelf storage:

• A shelf-resident volume can be either an optical or tape cartridge that is associated with stand-alone tape drives or operator-accessible optical drives within a pseudo library. The optical volume is physically stored on a shelf location near the drives that are associated with the pseudo-library to which the volume is assigned. The tape volume is physically stored on a shelf location near the drives that are associated with the TAPEUNITNAME parameter to which the volume is assigned.
• Assigning an object to storage class shelf (through an OSREQ STORE/CHANGE request or a class transition) does not cause the object to be physically moved to another volume. (The storage class ID row in the object directory table is the only change that is made.) Nor does the volume, on which the object resides, automatically get ejected from the library to which it is associated, even if all the objects on the volume indicate the storage class shelf. There is no storage class definition for shelf storage (no specific IARS value specific to shelf). This storage class assignment allows an installation a way of differentiating between performance objectives for objects that are actively accessed and those that must be archived, or those that are accessed the least. According to their storage management policy, the installation determines whether these objects having a storage class of shelf should be removed from the library and placed physically on a shelf location for storage.