Method and system for reading data from and writing data to a jukebox using a cache

• US 5,845,104 A
• Filed: 11/13/1995
• Issued: 12/01/1998
• Est. Priority Date: 11/13/1995
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Chemical Medience Corporation (Mitsubishi Chemical Group Corp.)
• Original Assignee: Mitsubishi Chemical Medience Corporation (Mitsubishi Chemical Group Corp.)
• Inventors: Rao, Mahesh Chandra
• Primary Examiner(s): Swann, Tod R.
• Assistant Examiner(s): LANGJAHR, DAVID
• Application Number:
  US08/554,981
• Time in Patent Office: 1,114 Days
• Field of Search: 395/622, 395/438, 395/404, 369/30
• US Class Current: 711/113
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 2003/0697 device management, e.g. handlers, drivers, I/O schedulers
• CPC Class Codes: G06F 3/0601 Interfaces specially adapted for storage systems

Abstract

A method and system for improving the transfer performance of a jukebox containing multiple media, either single-sided or double-sided, which, although independent, act as a single contiguous drive or volume. By caching writes in one embodiment and caching reads and writes in another embodiment, performance increases by preventing unnecessary disc swapping between the drive or drives of the jukebox. In operation, writes to the media currently in the drive are written through to the media and writes to all other media are cached while the cache does not have a predetermined utilization. When the cache has the predetermined utilization, a different media is placed in the drive and any cached or pending writes for the newly inserted media are sent to the newly inserted media and any corresponding cache entries are cleared.

Claims

1. A system for reading data from and writing data to a jukebox including at least one drive and plural removable media, the system comprising:

a cache including plural entries for storing sectors corresponding to sectors on the plural removable media; and

a controller for reading data from and writing data to the cache, the controller comprising;

means for writing data to the cache when a current media in the at least one drive does not contain a sector to be written,

means for writing data to a sector of the current media when the current media contains the sector to be written, and

means for flushing the cache to respective media.

2. The system according to claim 1, wherein the means for flushing the cache comprises a means for flushing the cache to respective media when the cache is at a predetermined utilization but is not full.

3. The system according to claim 1, wherein the means for flushing the cache comprises a means for flushing the cache to respective media when the number of cached writes to any one media is higher than a threshold.

4. The system according to claim 1, wherein the cache comprises:

a cache on a hard disk for storing most frequently used sectors;

a RAM cache for caching less frequently used sectors; and

a reference counting unit for reference counting accesses to sectors to determine assignments to the hard disk and RAM cache; and

wherein the means for writing comprises means for writing a sector to one of the cache on the hard disk and the RAM cache based on the reference count for the sector.

5. A system for reading data from and writing data to a jukebox including at least one drive and plural removable media, the system comprising:

a cache including plural entries for storing sectors corresponding to sectors on the plural removable media;

means for initializing the cache;

means for receiving a media request;

means for determining a type of the received media request as one of a read and write request;

means for reading and returning a sector from the cache if the read request requests a sector stored in the cache;

means for reading and returning a sector from a current media in the at least one drive if the read request requests a sector stored on the current media;

first means for changing to a new media;

means for returning data of a sector from the new media;

means for writing data of a sector to the current media if the write request requests data of a sector on the current media be stored;

means for writing data of a sector to the cache if the write request requests that data of a sector not on the current media be stored and the cache does not have a predetermined utilization;

second means for changing to a new media when the cache has a predetermined utilization; and

means for writing data of a sector from the cache to the new media.

6. The system according to claim 5, wherein the first means for changing to a new media comprises:

means for ejecting the current media from the at least one drive if the read request is for data of a sector not stored in the cache and not stored on the current media;

means for determining a new media to be inserted into the at least one drive if the read request is for data of a sector not stored in the cache and not stored on the current media; and

means for inserting the new media.

7. The system according to claim 5, wherein the second means for changing to a new media comprises:

means for ejecting the current media from the at least one drive if the write request is for data of a sector not stored in the cache and not stored on the current media when the cache has a predetermined utilization;

means for determining a new media to be inserted into the at least one drive if the write request is for data of a sector not stored in the cache and not stored on the current media when the cache has a predetermined utilization; and

means for inserting the new media.

8. The system of claim 6, wherein the first means for changing to a new media further comprises:

means for reordering and executing any additional requests for the current media in the at least one drive if the read request is for data of a sector not stored in the cache and not stored on the current media.

9. The system of claim 7, wherein the second means for changing to a new media further comprises:

means for reordering and executing any additional requests for the current media in the at least one drive if the write request is for data of a sector not stored in the cache and not stored on the current media when the cache has a predetermined utilization.

10. The system according to claim 6, wherein the first means for changing to a new media further comprises:

means for flushing any cached write requests for the new media to the new media; and

means for clearing from the cache any sectors corresponding to the cached write requests flushed to the new media.

11. The system according to claim 7, wherein the second means for changing to a new media further comprises:

means for flushing any cached write requests for the new media to the new media; and

means for clearing from the cache any sectors corresponding to the cached write requests flushed to the new media.

12. The system according to claim 6, wherein the means for determining a new media to be inserted comprises:

means for determining which of said plural removable media stores data of a sector corresponding to the read request.

13. The system according to claim 7, wherein the means for determining a new media to be inserted comprises:

means for determining which of said plural removable media stores data of a sector corresponding to the write request.

14. The system according to claim 7, wherein the means for determining a new media to be inserted comprises:

means for determining the media corresponding to the greatest number of cached writes.

15. The system according to claim 7, wherein the means for determining a new media to be inserted comprises:

means for determining the oldest cached sector in the cache.

16. The system according to claim 5, wherein the cache comprises a RAM cache.

17. The system according to claim 5, wherein the cache comprises a hard disk.

18. The system according to claim 5, wherein the cache comprises a flash memory.

19. A control system for caching writes to a jukebox including at least one drive and plural removable media, the control system comprising:

a cache;

means for writing data to the cache when a current media in the at least one drive does not contain a sector to be written;

means for writing data to a sector of the current media when the current media contains the sector to be written; and

means for flushing the cache to respective media.

20. The system according to claim 19, wherein the means for flushing the cache comprises a means for flushing the cache to respective media when the cache is at a predetermined utilization but is not full.

21. The system according to claim 19, wherein the means for flushing the cache comprises a means for flushing the cache to respective media when the number of cached writes to any one media is higher than a threshold.

22. The system according to claim 19, wherein the cache comprises:

a cache on a hard disk for storing most frequently used sectors;

a RAM cache for caching less frequently used sectors; and

a reference counting unit for reference counting accesses to sectors to determine assignments to the hard disk and RAM cache; and

wherein the means for writing comprises means for writing a sector to one of the cache on the hard disk and the RAM cache based on the reference count for the sector.