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.