Data storage system with data mirroring and reduced access time data retrieval

• US 5,390,313 A
• Filed: 09/24/1990
• Issued: 02/14/1995
• Est. Priority Date: 09/24/1990
• Status: Expired due to Term

• Current Assignee: EMC Corporation (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Vishlitzky, Natan, Alterescu, Bruno, Yanai, Moshe, Castel, Daniel
• Primary Examiner(s): Dixon, Joseph L.
• Assistant Examiner(s): PEIKARI, BEHZAD
• Application Number:
  US07/587,026
• Time in Patent Office: 1,604 Days
• Field of Search: 395/425, 395/575, 360/73.01, 360/73.07, 360/97.01, 360/98.01, 360/98.07, 360/47, 371/40.1, 371/51.1, 364/268.3, 364/268.5, 364/DIG. 1
• US Class Current: 711/112
• CPC Class Codes: G11B 20/1803 by redundancy in data representation
• CPC Class Codes: G11B 21/083 on discs
• CPC Class Codes: G11B 5/5547 "Seek" control and circuits therefor G11B5/5556 takes precedence
• CPC Class Codes: G11C 29/74 using duplex memories, i.e. using dual copies

Abstract

A data storage system with data mirroring and reduced access time data retrieval includes at least one pair of rotating data storage media each having a plurality of generally identical data records. Each rotating data storage medium includes position indicators, for providing one or more indications of the rotational position of each of the rotating data storage media with respect to its associated fixed position read/write mechanism. A position monitor receives the rotational position indications from each rotating data storage medium and computes and monitors the rotational position of each rotating storage medium with respect to its associated read/write mechanism. After receiving a request for access to one or more data records stored on the pair of rotating data storage media, the system computes projected data access times for retrieving the requested data record on each of the rotating data storage media, and commands retrieval of the requested data record to the rotating data storage medium having the shortest projected data access time based on the rotational position and state of the respective data storage medium.

Claims

1. A system for reducing data access time comprising:

at least first and second selectable rotating data storage media, each of said rotating data storage media having a rotationally fixed position read/write mechanism, each of said rotating data storage media also including at least a plurality of generally identical data records, said first rotating data storage medium having a rotational phase relationship with said second rotating data storage medium such that said first rotating data storage medium is rotating out of phase with respect to said second rotating data storage medium;

each of said rotating data storage media further including indicator means, for providing an indication of the rotational position of each rotating data storage medium with respect to its associated fixed position read/write mechanism;

means, responsive to at least one said rotational position indication provided by each of said first and second rotating data storage media, for controlling said rotational phase relationship of said first and second rotating data storage media relative to each other, and for assuring that said first and second rotating data storage media are rotating out of phase with each other;

means for receiving a single command to write at least one data record to one of said first and second rotating data storage media;

means, responsive to said received single command to write said at least one data record, for issuing a first write command to write said at least one data record to said first rotating data storage medium, and for independently issuing a second write command to write said at least one data record to said second rotating data storage medium;

wherein said second rotating data storage medium is available for data access during the issuance of said first write command to said first rotating data storage medium, and said first rotating data storage medium is available for data access during issuance of said second write command to said second rotating data storage medium;

position monitoring means, responsive to said rotational position indication from each of said rotating data storage media, for computing and monitoring the rotational position of each of said rotating data storage media with respect to its associated read/write mechanism;

means for receiving a request for access to said at least one data record stored on said first and second rotating data storage media; and

means, responsive to said position monitoring means and to said means for receiving a request for data access, for computing said first and second projected data access times for said first and second rotating storage media, and for directing retrieval of the at least one requested data record to said first or second rotating data storage medium having the shortest projected data access time.

2. The system of claim 1 wherein said rotating data storage medium includes a disk drive.

3. The system of claim 2 wherein said disk drive includes a fixed block disk drive.

4. The system of claim 1 wherein said at least one requested data record includes at least one address at which the data record is stored on said rotating storage media.

5. The system of claim 1 wherein said at least one requested data record includes a record identification portion and wherein said means for computing first and second projected data access times computes the address of the requested data on the first and second rotating data storage media.

6. The system of claim 5 wherein said requested data record includes a CKD formatted data record including at least a count portion, and wherein said means for computing computes, from the count portion of said CKD formatted data record, the address for each of said requested data records stored on said first and second rotating data storage media.

7. The system of claim 1 wherein said means for controlling maintains said first rotating data storage medium 180°

out of phase with said second rotating data storage medium.

8. The system of claim 1 wherein said position monitoring means includes a counter responsive to said at least one rotational position indication.

9. The system of claim 1 wherein said rotational position indicator means includes a plurality of reference marks generally equally spaced around each of said rotating data storage medium.

10. The system of claim 1 wherein said rotational position indicator means includes an index mark, for indicating the physical beginning of each of the rotating data storage media.

11. A system for reducing data access time on a pair of disk drive storage units having rotationally fixed position read/write mechanisms and data-mirroring, comprising:

at least first and second selectable disk drives, each of said disk drives including a plurality of generally identical data records, said first disk drive having a phase relationship with said second disk drive, such that said first disk drive is rotating out of phase with respect to said second disk drive;

means, responsive to at least one rotational position indication provided by each of said first and second disk drives, for controlling said phase relationship of said first and second disk drives relative to each other, and for assuring that said first and second disk drives are rotating out of phase with each other;

means for receiving a single command to write at least one data record to one of said first and second disk drives;

means, responsive to said received single command to write at least one data record, for issuing a first write command to write said at least one data record to said first disk drive, and for independently issuing a second write command to write said at least one data record to said second disk drive;

wherein said second rotating data storage medium is available for data access during the issuance of said first write command to said first rotating storage medium, and said first rotating data storage medium is available for data access during issuance of said second write command to said second rotating data storage medium,

each of said disk drives also including indicator means, including a plurality of reference marks generally equally spaced around each of said disk drive storage units, for providing a corresponding plurality of indications of the rotational position of each of the disk drives with respect to its associated rotationally fixed position read/write mechanism;

position monitoring means, responsive to said corresponding plurality of rotational position indications, for computing and monitoring the rotational position of each of said first and second disk drives;

means for receiving a request for access to said at least one data record stored on said first and second disk drives, said at lease one requested data record identified by a record identifier, for uniquely identifying said at least one data record from among a plurality of data records;

means, responsive to said means for receiving, for computing from said at least one record identifier, at least one address on said first and second disk drives at which said at least one requested data record is located; and

means, responsive of said position monitoring means and to said means for computing, for calculating first and second projected data access times for accessing said requested data records on each of said first and second disk drives, and or directing data retrieval to said first or second disk drive having the shortest projected data access time.

12. A method for reducing data access time on a pair of rotating data storage media including first and second selectable rotating storage media each having a plurality of tracks, and including a plurality of generally identical data records, each of said rotating data storage media having at least one rotationally fixed position read/write mechanism, said first rotating data storage medium having a rotational phase relationship with said second rotating data storage medium such that said first rotating data storage medium is rotating out of phase with respect to said second rotating data storage medium, comprising the steps of:

monitoring the rotational position of said first and second rotating data storage media with respect to their associated rotationally fixed position read/write mechanism;

monitoring the read/write mechanism position of said first and second rotating data storage media with respect to at least one track;

controlling said rotational phase relationship between said first and second rotating data storage media in response to said step of monitoring the rotational position of said first and second rotating data storage media, and assuring that said first and second rotating data storage media are rotating out of phase with each other;

receiving a single command to write at least one data record to said first and second rotating data storage media;

storing said at least one data record to be written to said first and second rotating data storage media in memory;

issuing, in response to said received single command to write said at least one data record, a first write command to cause said at least one data record stored in said memory to write out said first rotating data storage medium and, independently issuing a second write command to cause said at least one data record stored in said memory to be written to said second rotating data storage medium wherein said second rotating data storage medium is available for data access during the issuance of said first write command to said first rotating data storage medium, and said first rotating data storage medium is available for data access during issuance of said second write command to said second rotating data storage media;

receiving a request for access to said at least one data record stored on said first and second rotating data storage media;

computing first and second projected data access times for accessing the at least one requested data record for said at least one of first and second rotating data storage media;

comparing said first and second projected data access times to determine the shortest data access time for said requested data record; and

directing the rotating data storage medium with the shortest data access time to retrieve the at least one requested data record.

13. The method of claim 12 further including after the step of receiving a request for access to at least one data record the step of:

computing the address on the first and second rotating data storage medium at which the at least one requested data record is respectively stored.

14. A system for reducing data access time comprising:

at least first and second selectable rotating data storage media, each of said rotating data storage media having a rotationally fixed position read/write mechanism, each of said rotating data storage media also including at least a plurality of generally identical data records, said first rotating data storage medium having a rotational phase relationship with said second rotating data storage medium, such that said first rotating data storage medium is rotating out of phase with respect to said second rotating data storage medium;

means, responsive to at least one rotational position indication provided by each of said at least first and second rotating data storage media, for controlling said rotational phase relationship of said at least first and second rotating data storage media relative to each other, and for assuring that said at least first and second rotating data storage media are rotating out of phase with each other;

means for receiving a single command to write at least one data record to one of said first and second rotating data storage media;

means, responsive to said received single command to write said at least one data record, for issuing a first write command to write said at least one data record to said first rotating data storage medium, and for independently issuing a second write command to write said at least one data record to said second rotating data storage medium;

wherein said second rotating data storage medium is available for data access during the issuance of said first write command first rotating data storage medium, and said first rotating data storage medium is available for data access during issuance of said second write command to said second rotating data storage medium;

means for receiving a request for access to said at least one data record stored on said first and second rotating data storage media; and

means, responsive to said means for receiving a request for data access, for computing first and second projected data access times for said first and second rotating data storage media, and for directing retrieval of the at least one requested data record to said first or second rotating data storage medium having the shortest projected data access time.