Method and apparatus for independent and simultaneous access to a common data set

• US 6,542,974 B2
• Filed: 04/08/2002
• Issued: 04/01/2003
• Est. Priority Date: 04/30/1999
• Status: Expired due to Term

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Vishlitzky, Natan, Kopylovitz, Haim, Ofek, Yuval, Gagne, Mathieu
• Primary Examiner(s): Yoo, Do Hyun
• Assistant Examiner(s): Namazi, Mehdi
• Application Number:
  US10/118,518
• Publication Number:
  US 20020112133A1
• Time in Patent Office: 358 Days
• Field of Search: 711/117-118, 711/154, 711/162, 711/168, 710/39, 710/52, 714/6
• US Class Current: 711/154
• CPC Class Codes: G06F 11/1451 by selection of backup contents
• CPC Class Codes: G06F 11/2069 Management of state, configuration or failover
• CPC Class Codes: G06F 11/2082 Data synchronisation
• CPC Class Codes: G06F 3/0613 in relation to throughput
• CPC Class Codes: G06F 3/065 Replication mechanisms
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]

Abstract

A method and apparatus for enabling a common data set to be utilized by multiple data processes. During a first operating mode, first and second data stores in a data storage facility with a common buffer attach to a first data process and act as mirrors. Data to be written transfers to the common buffer and then to the data stores. A second command produces a split whereby the first data store remains attached to the first data process and the second data store is available to the second data process. After the second command is executed, any data in the common buffer is transferred to the corresponding data stores in parallel with and transparently to the actions between the first and second data processes and the first and second data stores, respectively.

Claims

1. A data storage facility with first and second data stores means, and a buffer means in which first and second data processes manipulate common data comprising:

A) pending write controller means responsive to a write request from a data process for identifying a specific location being transferred to said buffer means as a pending write request with the data associated with the pending write request thereafter being transferred to the specific location at a corresponding data store,

B) means for establishing a first operating mode during which the second data store means acts as a mirror for the first data store means that interacts with the first data process,

C) operating mode means for transferring the operation of the storage facility from the first operating mode to a second operating mode during which said second data store means interacts with the second data process and ceases to act as mirror for said first data store means, and

D) control means for controlling the processing of all pending write requests during the second operating mode at the time said operating mode means effects the transfer to the second operating mode, said pending write request controller means operating in parallel with and transparently to the interaction between the first and second data store means with the first and second data processes, respectively.

2. A data storage facility as recited in claim 1 wherein each of said data stores means has addressed locations and said operating mode means includes:

i) first processing means for processing of any pending write operations in the buffer means in an ordered fashion in parallel with and asynchronously with respect to operations between the data processes and their respective data stores means, and

ii) second processing means responsive to a predetermined data transfer request to an addressed location from the first and second data stores for processing any pending write operation in an area of the buffer means that is assigned to that addressed location.

3. A data storage facility as recited in claim 2 wherein the predetermined data transfer request includes write commands from the first and second data processes and read commands from the second data process, said second processing means including decoding means for decoding data transfer request for the predetermined requests.

4. A data storage facility as recited in claim 3 including, for each data store and for each addressed location in the data store, means for defining a table of flags including at least one write-pending flag that identifies each write request pending in the buffer means and a second flag indicating that specific track to be processed by the second processing means, each write data transfer request normally transferring the request to the buffer means and updating a corresponding write-pending flag.

5. A data storage facility as recited in claim 4 including additional flags and means for updating the state of the additional flags in response to the status of the write pending flags, said first and second processing means enabling said updating means.

6. A data storage facility as recited in claim 5 including means for generating a duplicate cache slot in response to predetermined states of the write pending flags.

7. A data storage facility that controls data transfers in a data processing system with first and second data processors and that includes first and second data stores and a buffer, the data storage facility responding to a predetermined transfer request by transferring data to a write pending location in the buffer and thereafter transferring the data to the data stores whereby during a first operating mode the first and second data stores act as mirror memories, said data storage facility including a control initiated upon receipt of a predetermined command for connecting the second data store for operation with the second data processor in parallel with continued operations between the first data store and the first data processor, said control comprising:

A) means for maintaining, during the first operating mode, an identification of all write pending locations for data to be transferred from the buffer to the second data store,

B) means for establishing a temporary operating mode in response to the predetermined command to connect the second data store to operate with the second processor and isolate the second data store from the first processor,

C) means for establishing a list of all write pending locations for data to be transferred to the second data store upon the establishment of the temporary operating mode, and

D) transfer means operable during the temporary operating mode for responding to data transfer requests for data in a write pending data location in the list in either of the first and second data stores thereby to effect a transfer of the data to the second data store.