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Cache Organization for Hierarchical Storage Systems

The hierarchical, storage management system consists of at least three or four
types of storage as follows:

 System memory
 Cache On-line high-speed magnetic disk storage
 Near-line optical disk libraries
 Off-line optical tape storage

 Many Cache designs use a high-water mark and a low-water mark to
trigger cache management operations. When the cache storage fills up to
the high-water mark, the cache manager starts creating more space in cache
storage. Space is created by discarding objects.
 The cache manager maintains a data base of objects in the cache. Cache
areas containing updated objects are frequently called dirty cache.
 Objects in dirty cache are written back at predetermined time intervals or
before discarding an object.

Difference between Magnetic Disk and Optical Disk

S.NO. MAGNETIC DISK OPTICAL DISK

1 Media type used is Multiple fixed disk Media type used is Single removable
disk

2 Intermediate signal to noise ratio Excellent signal to noise ratio

3 Sample rate is Low Sample rate is High

4 Implemented where data is randomly Implemented in streaming files.
accessed.

5 Only one disk can be used at a time Mass replication is possible

6 Tracks in the magnetic disk are In optical disk the tracks are
generally circular constructed spirally.

7 The data in the magnetic disk is In the optical disk, the data is
randomly accessed. sequentially accessed.

8 In the magnetic disk, only one disk is Optical disk allows mass replication
accessed at a time.