Method and apparatus for reading data from mirrored logical volumes on physical disk drives

• US 5,819,310 A
• Filed: 05/24/1996
• Issued: 10/06/1998
• Est. Priority Date: 05/24/1996
• Status: Expired due to Term

• Current Assignee: EMC Corporation (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Vishlitzky, Natan, Ofek, Yuval, Bachmat, Eitan
• Primary Examiner(s): Chan, Eddie P.
• Assistant Examiner(s): BRAGDON, REGINALD GLENWOOD
• Application Number:
  US08/653,154
• Time in Patent Office: 865 Days
• Field of Search: 711/114, 711/162, 395/182.04
• US Class Current: 711/114
• CPC Class Codes: G06F 11/2061 combined with de-clustering of data
• CPC Class Codes: G06F 11/2071 using a plurality of controllers
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 2212/312 In storage controller

Abstract

A mirrored memory for a data processing system. The memory system includes two device controllers and related disk drives for storing the mirrored data. Each of the disk drives is divided into logical volumes. Each device controller contains a plurality of reading processes and a correspondence table that establishes the reading process to be used in retrieving data from the corresponding disk drive. Each disk controller responds to a read command that identifies the logical volume by using the correspondence table to select the appropriate reading process and by transferring data from appropriate physical storage device containing the designated logical volume.

Claims

1. A mirrored memory system for retrieving data in response to a read command comprising:

(A) at least a pair of physical storage devices for storing redundant copies of related data in a mirrored fashion in a logical volume on each of the physical storage devices, each read command designating a logical volume from which data is to be retrieved,

(B) means for defining at least one reading process by which data can be transferred in response to a read command,

(C) a correspondency that assigns to each logical volume the reading process by which data is to be read from a physical storage device, and

(D) data transfer control means operable in response to said correspondency and said reading process definition means and connected to said physical storage devices for responding to a logical volume identification in a read command and the assignment from said correspondency by enabling the transfer of data from said physical storage devices containing the mirrored logical volumes according to the assigned reading process.

2. A memory system as recited in claim 1 wherein each logical volume consists of a set of contiguous tracks on a corresponding physical storage device, said reading process definition means establishes a reading operation for retrieving data in the logical volume from one of the physical storage devices and said correspondency assigns the reading process to only one of the physical storage devices whereby all data read from the logical volume is retrieved from the one physical storage device.

3. A memory system as recited in claim 1 wherein said reading process definition means establishes complementary reading operations for different portions of a logical volume and said correspondency assigns complementary reading processes to each physical storage device that stores the logical volume whereby data read from one logical volume is retrieved from at least two of said physical storage devices.

4. A memory system as recited in claim 3 additionally comprising means for establishing in said correspondency for each physical storage device a relationship between a logical volume contained therein and one of the complementary reading processes.

5. A memory system as recited in claim 1 wherein said data transfer control means includes a data transfer controller for each of said physical storage devices, said reading process definition means includes reading process identifications in each of said data transfer controllers and said correspondency includes in each of said data transfer controllers a correspondency table that defines for a logical volume, the reading process assigned for retrieving the data from the physical storage device.

6. A memory system as recited in claim 5 additionally comprising means for transferring entries to said correspondency tables.

7. In a data processing system including a data processor for generating a read command and a memory system for transferring data in response to the read command, said memory system comprising:

(A) a first physical disk drive and a second physical disk drive, each of said first and second physical disk drives being divided into at least one logical volume whereby a logical volume on the second physical disk drive mirrors the logical volume on the first physical disk drive,

(B) a first device controller connected between said first physical disk drive and the data processor and a second device controller connected between said second physical disk drive and the data processor, each of said device controllers being adapted to respond to the receipt of a read command identifying said first and second physical disk drives, respectively and each of said device controllers having a memory for storing information and programs including at least one reading process program for controlling a transfer from the physical disk drive and having a control unit for controlling transfers with physical disk drives connected thereto including means for executing the programs,

(C) a correspondency table in the memory of each of said device controllers that establishes the reading process program to be used in transferring data from a logical volume through said device controller, a control unit being responsive to the receipt of a read command and identification of one reading process program for transferring data from a logical volume through said device controllers with said control unit.

8. A data processing system as recited in claim 7 wherein each of said first and second physical disk drives stores another logical volume divided into first and second sections and wherein a correspondency table assigns the first section to be read by said first device controller from said first physical disk drive and the second section to be read by said second device controller from said second physical disk drive.

9. A data processing system as recited in claim 7 wherein one mirrored physical disk drive connected to each of said device controllers has a plurality of logical volumes, each comprising a plurality of contiguous tracks.

10. A data processing system as recited in claim 9 additionally comprising means connected to said device controllers for transferring entries to said correspondency tables.

11. A data processing system comprising:

(A) system bus means for enabling transfers,

(B) system memory means for storing data and commands connected to said system bus means, said system memory means including a cache memory and a command memory for receiving a read command from said system bus,

(C) at least one host adapter connected to said system bus including a data processor for executing applications and for issuing read commands, said host adapter having memory manager means for effecting a transfer of a read command over said system bus to said command memory,

(D) first and second physical disk drive means for storing information thereon, each of said first and second physical disk drives being divided into a plurality of logical volumes comprising a number of contiguous tracks whereby a logical volume in said second physical disk drive mirrors a corresponding logical volume in said first physical disk drive and

(E) first and second device controller means for controlling transfers with said first and second physical disk drives, respectively, each of said device controller means including;

(i) a memory manager for controlling transfers between a corresponding device controller means and said system memory means,

(ii) buffer memory means for storing data being transferred with a corresponding physical disk drive means,

(iii) control means connected to connected physical disk drive means and said buffer memory means for controlling the transfer of information therebetween according to at least one selectable reading process, and

(iv) a correspondence table having a read mode field identifying a reading process for each logical volume attached to said device controller means, said control means being responsive to the receipt of a read command identifying a logical volume connected to said physical disk drive control means for effecting a transfer from the connected one of said mirrored physical disk drives according to the read mode field.

12. A data processing system as recited in claim 11 wherein said information read from one of said mirrored physical disk drives is transferred by said corresponding device controller means to said cache memory in said system memory means, said corresponding device controller means additionally transferring information to said command memory in said system memory means for enabling said host adapter to retrieve said information.

13. A data processing system as recited in claim 12 wherein each of a pair of mirrored logical volumes is divided into a first section of contiguous tracks and a second section of the remaining contiguous tracks in said logical volume and wherein said read mode field can include another value that causes said corresponding device controller to respond by determining if that device controller and connected physical disk drive should perform the read operation from a specified section of contiguous tracks.

14. A data processing system as recited in claim 12 wherein said system memory responds to the receipt of a read command by:

(i) transferring the requested information when that information is located in said cache memory of said system memory, and

(ii) initiating the reading operation from a logical volume when that information is absent from said cache memory in said system memory.

15. A data processing system as recited in claim 14 additionally comprising a system manager means for transferring information over said system bus means to said host adapter and first or second device controller means, said system manager means including means for establishing said read mode fields in each of said correspondence tables.

16. A data processing system as recited in claim 15 further comprising bus access logic means for controlling the transfer of information over the system bus means.

17. A method for transferring in response to a read command, data from one of mirrored physical storage devices comprising the steps of:

(A) storing on each of at least a pair of physical storage devices redundant copies of related data in a mirrored fashion in a logical volume on each of the physical storage devices, each read command designating a logical volume from which data is to be retrieved,

(B) defining at least one reading process by which data can be transferred in response to a read command,

(C) assigning in a correspondency a reading process by which data in a logical volume is to be transferred from a physical storage device, and

(D) determining in response to the logical volume identified in a read command and the reading process identified by said correspondency assignment the process by which the data will be transferred from each of the physical storage devices containing the mirrored logical volume.

18. A method as recited in claim 17 wherein a logical volume consists of a set of contiguous tracks on each physical storage device and one of the at least one reading processes establishes a reading operation for retrieving data for a logical volume from a designated one of the physical storage devices, said correspondency assignment step establishing which of the pair of physical storage devices is to provide the data and said determination step enabling data transfers in response to a read command identifying a logical volume from the designated one physical storage device.

19. A method as recited in claim 17 wherein said reading process definition step establishes complementary reading operations for different portions of a logical volume and said correspondency assignment step establishes complementary reading processes to each physical storage device that stores a logical volume whereby data from a logical volume is retrieved from at least two of the physical storage devices.

20. A method as recited in claim 19 additionally comprising a step of establishing in said correspondency assignment for each physical storage device a relationship between the logical storage volume contained therein and one of the complementary reading operations.

21. A method as recited in claim 17 wherein each of the physical storage devices connects to a device controller and wherein each device controller stores the reading processes and the correspondency assignments relevant thereto and performs said determining step to determine, in response to the selected reading process identified in the correspondency assignment, the reading process to be used by the device controller in response to a read command for the logical volume.

22. A method as recited in claim 21 additionally comprising a step of transferring entries to the correspondency assignments in each of the device controllers.

23. A method as recited in claim 22 additionally comprising a step of monitoring the performance of each device controller, one device controller performing a read operation when the operating status of an assigned device controller indicates its inability to perform.

24. A method for transferring, in response to a read command, data from mirrored memory systems for use in a data processing system including a system memory including a cache memory and a command memory for receiving a read command from a system bus, at least one host adapter connected to the system bus and adapted for connection to a data processor and having a cache memory manager for effecting a transfer of a read command over the system bus to the command memory, first and second physical disk drives for storing information thereon, and first and second device controllers for controlling transfers with the first and second physical disk drives, respectively, each of the device controllers including a cache memory manager for controlling transfers between the corresponding device controller and the system memory and including a buffer memory for storing data being transferred with the physical disk drive and a control connected to the physical disk drive and the buffer memory for controlling the transfer of information therebetween, said method comprising the steps of:

(A) storing in each of the first and second physical disk drives redundant copies of data in at least one logical volume comprising a number of contiguous tracks on each of the physical disk drives whereby a logical volume on the second physical disk drive mirrors the logical volume of the first physical disk drive,

(B) defining in each device controller selectable reading processes by which data is transferred from the physical disk drives connected to the device controller,

(C) establishing in each device controller a correspondence table having a read mode field for each logical volume attached to the device controller that identifies one of the selectable reading processes, and

(D) responding, in each device controller, to the receipt of a read command identifying a logical volume and the corresponding read mode field for effecting a transfer of the data in the logical volume from the connected one of the physical disk drives according to the selected reading process.

25. A method as recited in claim 24 wherein the device controller performing the transfer additionally transfers the information read from the corresponding physical disk drive to the cache memory in the system memory and transfers information to the command memory in the system memory means for enabling the host adapter to retrieve the information from the cache memory.

26. A method as recited in claim 25 wherein one of the mirrored logical volumes is divided into a first section of contiguous tracks and a second section of the remaining contiguous tracks in the one of the mirrored logical volumes and wherein the device controller responds to a certain value of the read mode field by determining if that device controller and connected physical disk drive should perform the read operation from the specified track.

27. A method as recited in claim 25 wherein the system memory responds to the receipt of a read command by:

(i) transferring the requested information when that information is located in the cache memory of the system memory, and

(ii) initiating the reading operation from the mirrored logical volumes when that information is absent from the cache memory in the system memory.

28. A method as recited in claim 27 additionally comprising a step of establishing the read mode fields in each of the correspondence tables.

29. A method as recited in claim 28 additionally comprising the step of controlling the transfer of information over the system bus.