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Hierarchical Storage Management

multi-function drive is a single drive unit. It is capable of reading and writing a
variety of disk media. Three types of technologies are used for multi-function
drives. They are:

(i) Magneto-optical disk for both rewritable and WORM capability.
(ii) Magneto-optical disk for rewritable and dye polymer disk for WORM
capability.
(iii) Phase change technology for both rewritable and WORM capability.

The storage hierarchies described in the pyramid consist of random-access
memory (RAM), on-line fast magnetic hard disks, optical disks and juke boxes,

diskettes, and tapes.

Permanent Vs. Transient Storage issues

The process of moving an object from one level in the storage hierarchy to another
level in that hierarchy is called migration. Migration to objects to off-line media
and removal of these objects from on-line media is called archiving. Migration
Can be set up to be manual or automatic. Manual migration requires the user or
the system administrator to move objects from one level of storage to another
level. Systems with automatic migration perform this task automatically. In
document-imaging systems, compressed image files are created in magnetic
cache areas on fast storage devices when documents are scanned.

Optical Disk Library (Juke box)

An optical juke box stacks disk platter to be played. In the optical disk library,
the platters are optical and contain objects such as data, audio, video, and images.

An optical disk library has one or more optical drives. An optical disk library uses
a very-high-speed and accurate server-controlled electromechanical robotics
elevator mechanism for moving the optical platters between their slots on a disk
stacks and the drives. The robotics mechanism removes disk platter from a drive
and returns it to its slots on the stack after the disk has finished playing (usually
when the drive is required for another disk). The robotics device operates and
manages multiple drives under program control.

A juke box may contain drives of different types, including WORM, rewritable,
or multifunction. Juke boxes contain one or more drives. A juke box is used for
storing large volumes of multimedia information in one cost effective store. Juke
box-based optical disk libraries can be networked so that multiple users can
access the information. Optical disk libraries serve as near-line storage for
infrequently used data.