Method and apparatus for enhancing operations in disk array storage devices

• US 20030204692A1
• Filed: 04/29/2002
• Published: 10/30/2003
• Est. Priority Date: 04/29/2002
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Don, Arieh, LeCrone, Douglas E., Tamer, Philip E.
• Granted Patent: US 6,983,353 B2
• Time in Patent Office: Days
• US Class Current: 711/163
• 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
• CPC Class Codes: G06F 3/061 Improving I/O performance
• CPC Class Codes: G06F 3/0659 Command handling arrangements, e.g. command buffers, queues, command scheduling
• CPC Class Codes: G06F 3/0665 at area level, e.g. provisioning of virtual or logical volumes
• CPC Class Codes: G06F 3/0689 Disk arrays, e.g. RAID, JBOD

Abstract

A method and apparatus for assuring data consistency during certain operations involving dependent input/output sequences. During such operations a stall application blocks write operations to specified logical devices in a local consistency group while allowing read operations to all devices and write operations to non-specified logical devices. When a write command is directed to a logical device in local consistency group, the host adapter associated with the logical device returns a message to the host that initiates a write command retry. Retries generally continue until a write command is successful.

Claims

1. A method for maintaining data consistency in a group of logical devices wherein each logical device is adapted for normally responding to read and write commands issued by a host by performing a commanded operation and by transferring a message to the host indicating the outcome of the command operation, said method comprising the steps of:

A) establishing a plurality of the logical devices as a local consistency group with a reject window having an open state that extends for a predetermined interval and a closed state,

b) blocking, at a control for each logical device, any processing of a write command directed to a logical device in the defined consistency group while the reject window is in the open state, and

c) in response to said blocking, generating a predetermined return message to the host for a response thereto.

2. A method as recited in claim 1 wherein the host generates a setting command with a list of logical devices to be included in the local consistency group and a window size parameter that establishes the interval that the reject window is in its open state, said establishing of the local consistency group including defining the open state interval for each logical device in the local consistency group.

3. A method as recited in claim 2 wherein each logical device is associated with time clock and said establishing includes recording, for each logical device, the time defined by the time clock associated with that logical device.

4. A method as recited in claim 3 wherein said blocking of a write command to a logical device with local consistency group determines whether the time defined by the associated time clock at the time of the write command is concurrent with the open state of the reject window.

5. A method as recited in claim 3 wherein said establishment includes generating a data structure for each logical device in the local consistency group including a time stamp entry for receiving the time from the time clock associated with the corresponding logical device and a window size entry for receiving the window size.

6. A method as recited in claim 5 wherein in response to a write command to a logical device said blocking determines whether the time defined by the associated time clock at the time the write command is received is less than the time obtained by combining the time stamp and window size entries for the logical device identified in the write command.

7. A method as recited in claim 3 wherein the host generates an extension command with a list of logical devices included in the local consistency group, said method including the step responding to the extension command by replacing the recorded time for each logical device with the time defined by the time clock associated with that logical device when the extension command is processed for that logical device.

8. A method as recited in claim 2 wherein said establishment includes generating a data structure for each logical device in the local consistency group including a first flag for controlling the removal of the generated data structure, said method comprising removing the data structure for a logical device upon receipt of a write command to that logical device after the reject window returns to the closed state and in response to the state of the first flag.

9. A method as recited in claim 2 wherein said establishment includes generating a data structure for each logical device in the local consistency group and wherein the host generates a resetting command, said method additionally comprising the step of removing the data structures for all the logical devices in the local consistency group in response to the resetting command.

10. A method as recited in claim 9 wherein said removal step includes generating a message for transfer to the host for each logical device in which the reject window is in a closed state when the resetting command is processed for the corresponding logical device.

11. A method as recited in claim 10 wherein each logical device data structure includes a flag having a first state and a second state indicating that the logical device is a member of the local consistency group, said removal step including the step of generating a message when the flag is in the first state.

12. A method as recited in claim 2 wherein the setting command additionally includes a specific return message parameter that is returned as the predetermined message, the host being responsive to the message by issuing the write command again, said establishment including the step of generating a data structure for each logical device in the local consistency group including an entry for the specific return message to be sent when a write command is blocked.

13. A method as recited in claim 12 wherein the setting command additionally includes a reject delay parameter and said establishing includes the step storing the reject delay parameter in the data structure for each logical device in the local consistency group, said method additionally including the step of determining a delay between said blocking and said return message generation in response to said delay parameter.

14. A method as recited in claim 12 wherein the setting command additionally includes a reject delay parameter corresponding to a reject delay time interval and said establishing includes the step storing the reject delay parameter in the data structure for each logical device in the local consistency group, said method additionally including the step of delaying said return message generation until an interval corresponding to the reject delay time after said blocking of a write command.

15. A system for maintaining data consistency in a group of logical devices wherein each logical device is adapted for normally responding to read and write commands issued by a host by performing a commanded operation and by transferring a message to the host indicating the outcome of the commanded operation, said system comprising:

A) means for establishing a plurality of the logical devices as a local consistency group with a reject window having an open state that extends for a predetermined interval and a closed state,

B) means for blocking, at a control for each logical device, any processing of a write command to a logical device in the defined consistency group while the reject window is in the open state, and

C) means responsive to said blocking means for generating a predetermined return message to the host for a response thereto.

16. A system as recited in claim 15 wherein the host generates a setting command with a list of logical devices to be included in the local consistency group and a window size parameter that establishes the interval that the reject window is in its open state, said establishing means including means for defining the open state interval for each logical device in the local consistency group.

17. A system as recited in claim 16 wherein each logical device is associated with a time clock and said establishing means for includes recording, for each logical device, the time defined by the time clock associated with that logical device.

18. A system as recited in claim 17 wherein said blocking means for a logical device in a local consistency group includes means for determining whether the time defined by the associated time clock at the time of the write command is concurrent with of the open state of the reject window.

19. A system as recited in claim 17 wherein said establishing means includes means for defining a data structure for each logical device in the local consistency group including a time stamp entry for receiving the time from the clock associated with the corresponding logical device and a window size entry for receiving the window size.

20. A system as recited in claim 19 wherein said blocking means includes means responsive to the receipt of a write command for determining whether the time of the time clock associated with the logical device when the write command is received is less than the time obtained by combining the time stamp and window size entries for the logical device identified in the write command.

21. A system as recited in claim 17 wherein the host generates an extension command with a list of logical devices included in the local consistency group, said system including means for responding to the extension command by replacing the recorded time for each logical device with the time defined by the time clock associated with that logical device when the extension command is processed for that logical device.

22. A system as recited in claim 16 wherein said establishing means includes means for generating a data structure for each logical device in the local consistency group, said data structure including a first flag having first and second states for controlling the removal of the generated data structure, and means for removing the data structure for a logical device upon receipt of a write command to that logical device after the reject window returns to the closed state and when the flag is in the first state.

23. A system as recited in claim 16 wherein said establishing means includes means for generating a data structure for each logical device in the local consistency group and wherein the host generates a resetting command, said system additionally comprising means for removing the data structures for all the logical devices in the local consistency group in response to a resetting command.

24. A system as recited in claim 23 wherein said removal means includes means for generating a message for transfer to the host for each logical device in which the reject window is in a closed state at the time the resetting command is processed for the corresponding logical device.

25. A system as recited in claim 24 wherein each logical device data structure includes a flag having a first state and having a second state indicating that the logical device is a member of the local consistency group, said removal step including means for generating a message when said flag is in the first state.

26. A system as recited in claim 16 wherein the setting command additionally includes a specific return message that is returned as the predetermined message, the host being responsive to the message by issuing the write command again, said establishing means including means for generating a data structure for each logical device in the local consistency group including an entry for the specific return message to be sent when a write command is blocked.

27. A system as recited in claim 26 wherein the setting command additionally includes a reject delay parameter, said establishing means including means for storing the reject delay parameter in the data structure for each logical device in the local consistency group and said message generating means including means for producing a delay between the operation of said blocking means and the operation of said return message generating means in response to the reject delay parameter.

28. A system as recited in claim 26 wherein the setting command additionally includes a reject delay parameter corresponding to a reject delay time and said establishing means includes means for storing the reject delay parameter in the data structure for each logical device in the local consistency group, said message generating means including means for delaying the operation of said return message generating means for an interval corresponding to the reject delay time after said blocking means operates to block a write command.