Distributed, scalable data storage facility with cache memory

• US 20030159001A1
• Filed: 02/19/2002
• Published: 08/21/2003
• Est. Priority Date: 02/19/2002
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Niver, Brett D., Chalmer, Steven R., McClure, Steven T., Wheeler, Richard G.
• Granted Patent: US 6,757,790 B2
• Time in Patent Office: Days
• US Class Current: 711/120
• CPC Class Codes: G06F 12/0815 Cache consistency protocols
• 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
• CPC Class Codes: G06F 3/0613 in relation to throughput
• CPC Class Codes: G06F 3/0614 Improving the reliability of storage systems
• CPC Class Codes: G06F 3/0638 Organizing or formatting or addressing of data
• CPC Class Codes: G06F 3/0646 Horizontal data movement in storage systems, i.e. moving data in between storage devices or systems
• CPC Class Codes: G06F 3/0676 Magnetic disk device
• CPC Class Codes: G06F 3/0689 Disk arrays, e.g. RAID, JBOD

Abstract

The data storage facility includes a plurality of data storage devices coupled through multi-path connections to cache memory. A plurality of interfaces to host processors communicates with the cache memory and with cache tag controllers that define the cache memory again over multiple paths.

Claims

1. A data storage facility for operation with a plurality of data processors each of which can issue a host request to initiate a data transfer with the data storage facility, said data storage facility comprising:

A) a plurality of uniquely addressed data storage locations and controls for transferring data to and from the addressed locations,

B) a plurality of processor-controlled data handling nodes responsive to a host request for identifying a specific data storage location, said processor-controlled data handling nodes including cache memory storage at cache memory locations for the data identified in the host request,

C) processor-controlled cache tag controller nodes for maintaining cache tags that identify a specific cache location for each addressed data storage location in response to the processing of a data transfer request in said data handling nodes,

D) a first multi-path connection interconnecting said data handling nodes and said cache tag controller nodes, and

E) a second multi-path connection interconnecting said plurality of data storage locations and said cache memory locations.

2. A data storage facility as recited in claim 1 wherein the data storage location addresses occupy a common address space and wherein each said data handling node includes storage for address conversion information thereby to convert a host request address into an address for a specific data storage location in the common address space and said cache tag controller nodes contain information for converting the data storage location address into an address for a cache tag entry in the cache tag controller node and a corresponding cache memory location.

3. A data storage facility as recited in claim 2 wherein each data handling node identifies a cache memory location using multiple-field, cache-coherent protocol messages to effect transfers between the cache memory locations and the data storage locations in response to a host request, each said message including operation code, address, node identification, data length and data fields, the address field containing the address the specific data storage location in the common address space.

4. A data storage facility as recited in claim 3 adapted for operating with redundant paths for certain data transfers wherein each node identification field identifies a first data handling node with cache memory and a second, redundantly operating, data handling node with cache memory storage.

5. A data storage facility as recited in claim 3 wherein cache tag controller entry can be locked in response to a message from a data handling node to respond to messages only from the requesting data handling node and wherein said cache tag controller node responds to multiple-field, cache-coherent protocol messages that include operation code, address, node identification and lock owner fields, said lock owner field identifying a data handling node that holds any lock on the cache tag entry.

6. A data storage facility as recited in claim 2 wherein each of said cache memory locations and cache tag entries is characterized by one of four operating states including a non-existent state when the requested cache tag entry and cache memory location do not exist in any cache tag controller node or cache memory location, an invalid state when a cache tag entry exists but the corresponding cache memory location does not contain valid data, an exclusive state when a single cache memory location contains valid data and a modified-shared state when two cache memory locations contain the same valid data.

7. A data storage facility as recited in claim 6 wherein said cache tag controller node includes means responsive to certain request messages for generating one of a plurality of responses to each host request and wherein said cache tag controller node includes means responsive to certain request messages for altering the operating state for the corresponding cache memory and cache tag entry locations.

8. A data storage facility as recited in claim 7 wherein said cache tag controller node has a state control and a preexisting operating state for a cache tag entry and wherein said host request is a host read request for initiating a transfer of data from said data storage facility and wherein valid data is stored in the corresponding cache memory location, said state control leaving the preexisting operating state unchanged.

9. A data storage facility as recited in claim 7 wherein said cache tag controller node has a state control and wherein said host request is a host read request for initiating a transfer of data from said data storage facility and wherein said cache tag controller node includes means for identifying a cache tag entry and corresponding cache memory location for the host read request data by indicating in the cache tag entry and corresponding cache memory storage location that the cache memory location contains invalid data and transferring data from the said data storage locations to the cache memory location, said state control transferring the state from the non-existent state to the invalid state and then changing the state to the exclusive state after which the requested data transfers to the host from said cache memory location.

10. A data storage facility as recited in claim 7 wherein said cache tag controller node has a state control and a preexisting operating state for the cache node entry and wherein said host request is a host write request for initiating a transfer of data to said data storage facility and wherein valid data can be stored in the two corresponding cache memory locations, said state control establishing the modified-shared state.

11. A data storage facility as recited in claim 7 wherein said cache tag controller node has a state control and wherein said host request is a host write request for initiating a transfer of data to said data storage facility and wherein the state is the non-existent state, said cache tag controller identifying a cache tag entry and corresponding cache memory location for the data and said state control initially changing the state to an invalid state and then changing the state to a modified-shared state if the write request is successful, said data handling node generating a host return of success if the data successfully transfers to the addressed data storage location.

12. A data storage facility as recited in claim 1 wherein certain of said data handling devices constitute I/O nodes with a first interface for connection to a data processor and a second interface for connection to first multi-path connection.

13. A data storage facility as recited in claim 1 wherein certain of said data handling nodes constitute cache nodes with a first interface for connection to said first multi-path connection and a second interface for connection to said second multi-path connection.

14. A data storage facility as recited in claim 13 wherein the others of said data handling devices constitute I/O nodes, each I/O node having a first interface for connection to a data processor and a second interface for connection to first multi-path connection whereby said first and second multi-path connections provide first and second independent paths between said I/O nodes and said cache nodes and between said I/O nodes and said cache tag controller nodes and between said cache nodes and said data storage devices.

15. A data storage facility as recited in claim 14 wherein at least one of said first and second multi-path connections comprises a local area network.

16. A data storage facility as recited in claim 14 wherein at least one of said first and second multi-path connections comprises a wide-area network whereby individual ones of said I/O nodes, cache nodes and cache tag controller nodes can be located at a distance from each other.

17. A data storage facility as recited in claim 1 wherein each of said data handling nodes and said cache tag controller nodes comprises at least one processor, random access memory, first and second interfaces and an interconnecting bus.

18. A data storage facility as recited in claim 1 wherein each of said data handling nodes and said cache nodes comprises a processor module with first and second interfaces.

19. A data storage facility as recited in claim 18 wherein said processor module includes a plurality of processor modules.

20. A data storage facility as recited in claim 19 wherein at least one of the first and second interfaces connects to one of the first and second multi-path connections that comprises a local area network.

21. A data storage as recited in claim 19 wherein at least one of the first and second interfaces connects to one of the first and second multi-path connections that comprises a wide area network.

22. A data storage facility for operation with at least one data processor that issues host requests, said data storage facility comprising:

A) a plurality of data storage devices with a plurality of persistent data storage locations,

B) at least one of a first group of processor-controlled I/O nodes adapted for connection to at least one data processor, each said I/O node including means for converting an address in a host request to an address for a specific data storage location in the plurality of data storage devices,

C) a plurality of a second group of processor-controlled cache nodes, each said cache node including a memory adapted to operate as an independent cache memory for transferring data with storage locations in the plurality of data storage devices,

D) at least first and second processor-controlled cache tag controller nodes, said cache tag controller nodes being connected for parallel operation and each said cache tag controller node converting each address from said I/O nodes into a location that defines a cache tag entry location in the cache tag controller node and a corresponding location in the cache nodes,

E) a first multi-path connection interconnecting said I/O, cache and cache tag controller nodes, and

F) a second multi-path connection interconnecting said plurality of said data storage devices and said cache nodes whereby said data storage facility provides parallel paths for each data transfer in response to a data request.

23. A data storage facility as recited in claim 22 wherein the data storage location addresses occupy a common address space and wherein each said I/O node includes storage for address conversion information thereby to convert a host request address into an address for a specific data storage location in the common address space and each of the cache tag controller nodes contains information for converting the data storage location address into an address for a cache tag entry in the cache tag controller node and a corresponding cache memory location in a cache node.

24. A data storage facility as recited in claim 23 wherein each cache tag controller node identifies a cache memory location and cache tag entry location using multiple-field, cache-coherent protocol messages to effect transfers with the cache memory locations in the identified cache node and the requesting I/O node in response to a host request, each said message including operation code, address, node identification, data length and data fields, the address field containing the address the specific data storage location in the common address space.

25. A data storage facility as recited in claim 24 adapted for operating with redundant paths for certain data transfers wherein each node identification field identifies a first and second cache nodes for handling the data involved with the transfer.

26. A data storage facility as recited in claim 23 wherein cache tag controller entry can be locked in response to a message from one of the I/O and cache nodes to respond to respond to messages only from that node and wherein said cache tag controller node responds to multiple-field, cache-coherent protocol messages that include operation code, address, node identification and lock owner fields, said lock owner field identifying the node that holds any lock on the cache tag entry location.

27. A data storage facility as recited in claim 23 wherein each of said cache memory locations and cache tag entries is characterized by one of four operating states including a non-existent state when the requested cache tag entry and cache memory location do not exist in any cache tag controller node or cache memory location, an invalid state when a cache tag entry exists but the corresponding cache memory location does not contain valid data, an exclusive state when a single cache memory location contains valid data and a modified-shared state when two cache memory locations contain the same valid data.

28. A data storage facility as recited in claim 27 wherein said cache tag controller node includes means responsive to certain request messages for generating one of a plurality of responses to each host request and wherein said cache tag controller node includes means responsive to certain request messages for altering the operating state for the corresponding cache memory and cache tag entry locations.

29. A data storage facility as recited in claim 28 wherein said cache tag controller node has a state control and a preexisting operating state for a cache tag entry and wherein a host request is a host read request for initiating a transfer of data from said data storage facility and wherein valid data is stored in the corresponding cache memory location in a cache node, said state control leaving the preexisting operating state unchanged.

30. A data storage facility as recited in claim 28 wherein said cache tag controller node has a state control and wherein said host request is a host read request for initiating a transfer of data from said data storage facility and wherein said cache tag controller node includes means for identifying a cache tag entry and corresponding cache memory location for the host read request data by indicating in the cache tag entry and corresponding cache memory storage location that the cache memory location contains invalid data and transferring data from the said data storage locations to the cache memory location, said state control transferring the state from the non-existent state to the invalid state and then changing the state to the exclusive state after which said I/O node transfers the requested data to the host from said cache memory location in said cache node.

31. A data storage facility as recited in claim 28 wherein said cache tag controller node has a state control and a preexisting operating state for the cache memory location and corresponding cache tag entry and wherein said host request is a host write request for initiating a transfer of data to said data storage facility and wherein valid data can be stored in cache memory locations in two cache nodes, said state control establishing the modified-shared state.

32. A data storage facility as recited in claim 28 wherein said cache tag controller node has a state control and wherein said host request is a host write request for initiating a transfer of data to said data storage facility and wherein the state is the non-existent state, said cache tag controller identifying a cache tag entry and corresponding cache memory location in a cache node for the data and said state control initially changing the state to an invalid state and then changing the state to a modified-shared state if the write request is successful, said I/O node generating a host return of success if the data successfully transfers to the addressed locations in the cache nodes.

33. A data storage facility in claim 23 wherein in response to the receipt of a host write request said I/O node identifies multiple cache nodes for receiving the data to be transferred to a specific data storage location.

34. A data storage location as recited in claim 23 wherein said I/O node contains information identifying mirroring storage locations in said data storage devices and said I/O node includes means for generating an address for each mirroring storage location.

35. A data storage facility as recited in claim 23 wherein each cache node includes means for sending request messages to said cache tag controller nodes for terminating the relationship between a specific cache tag entry and corresponding cache node memory location and a data storage location address whereby each cache tag controller and cache node location can identify different data storage locations.

36. A method for transferring data in response to a host request with a data storage facility with a first plurality of persistent data storage locations having addresses in a first common address space, said method comprising:

A) establishing a second plurality of cache memory locations in another address space, each of which can store data,

B) establishing cache tag locations for each of the second plurality of cache memory locations, each cache tag location entry adapted to store a cache tag entry with status information about a corresponding cache memory location,

C) responding to each host request by;

i) converting an address in the data transfer request into an address in the first common address space,

ii) converting the address for the first common address space into an address for a cache tag entry location,

iii) testing the cache tag in the cache tag location to determine the presence of a cache memory location that corresponds to the location in the host request, and

iv) initiating a transfer of data with the corresponding cache memory location for predetermined values of the corresponding status information.

37. A method as recited in claim 36 wherein said method additionally comprises generating a sequence of request messages for obtaining the status of a cache memory location and generating response messages with the requested status.

38. A method as recited in claim 37 additionally comprising accepting a response message received within a predetermined timeout interval and instituting a retry operation by restarting the sequence of request messages when the response message is received after the predetermined timeout interval.

39. A method as recited in claim 37 additionally comprising counting each retry operation for a given host request and terminating the response to the host request if the count of retry operations exceeds a predetermined maximum and monitoring the response time that expires after an initial sequence begins to terminate the response to the host request if the response time exceeds a predetermined timeout interval.

40. A method as recited in claim 37 wherein certain of the request messages identify a cache tag entry location and others identify to a cache memory location.

41. A method as recited in claim 37 wherein a host request is a host read request for transferring data from a specific data storage location and wherein a first request message requests the status of the cache tag in the cache tag location corresponding to the address in the first common address space and the response message indicates whether the located cache tag corresponds to the requested address and is unlocked.

42. A method as recited in claim 41 wherein the response message indicates that the located cache tag entry corresponds to the requested address and is unlocked, said method additionally sending a second request message that initiates a transfer of the data in the specified cache memory location and generating a response message with the data for the response to the host read request.

43. A method as recited in claim 41 wherein the response message fails to indicate that the located cache tag corresponds to the requested address and is unlocked, said method additionally generating a second request message requesting the data to be transferred to the specified cache memory location from the corresponding data storage location and generating a response message with the data from the specified cache memory location.

44. A method as recited in claim 43 additionally comprising sending a third request message for unlocking the cache tag and generating a response message indicating the success of that operation.

45. A method as recited in claim 37 wherein a host request is a host write request with data for transfer to a specific data storage location, said method comprising generating a first request message identifying two cache memory locations for receiving the data in the host write request and requesting the status of each cache tag, and generating a response message indicating whether each located cache tag corresponds to the requested address and is locked for use in the specified transfer.

46. A method as recited in claim 45 wherein the response message indicates that the located cache tags correspond to the requested address and are locked for use in the specified transfer, said method comprising sending a second request message to each of the cache memory locations identified by the cache tags with the data from the host request.

47. A method as recited in claim 46 additionally comprising sending a response message to the second request message indicating success and sending a third request message to unlock the cache tag.

48. A method as recited in claim 47 wherein the cache tag locations and locations in the cache memory are characterized by operating states including exclusive and modified-shared operating states indicating only one location in one cache memory location or two cache memory locations, respectively, contain data for one data storage location, said method additionally comprising the step of responding to the third request message by updating the operating state for the selected cache memory location to a modified-shared state and by sending a response message.

49. A method as recited in claim 46 wherein the a plurality of data storage locations are to receive the data in the host write request, said method comprising sending a request message to lock the addressed cache tags and upon receipt of a response message indicating that success of that operation, determining if the data has been written to all the data storage locations by terminating the correspondence between the cache tag and the data storage location in the first common address space.

50. A method as recited in claim 37 additionally comprising monitoring the utilization of the cache memory, selecting a cache memory location that can be made available for other data storage locations and, in response to the selection, generating a first request message to lock the corresponding cache tag and upon receipt of a response message indicating that success of that operation, terminating the correspondence between the cache tag and the data storage location in the first common address space.

51. A data storage facility with a first plurality of persistent data storage locations having addresses in a first common address space for transferring data in response to host requests, said facility comprising:

A) a second plurality of cache memory locations in another address space, each of which can store data,

B) a cache tag location for each of the second plurality of cache memory locations, each cache tag location adapted to store a cache tag with status information about a corresponding cache memory location,

C) a control including;

i) first conversion means for converting an address in the data transfer request into an address in the first common address space,

ii) second conversion means for converting the address for the first common address space into an address for a cache tag entry location,

iii) testing means for testing the cache tag in the cache tag location to determine the presence of a cache memory location that corresponds to the location in the host request, and

iv) means for initiating a transfer of data with the corresponding cache memory location for predetermined values of the corresponding status information.

52. A data storage facility as recited in claim 51 additionally comprising means for generating a sequence of request messages for obtaining the status of a cache memory location and generating response messages with the requested status.

53. A data storage facility as recited in claim 52 additionally comprising means for defining a predetermined time internal during which a response message will be accepted and means for restarting the sequence of request messages when the response message is received after the predetermined timeout interval.

54. A data storage facility as recited in claim 52 additionally comprising means for counting each retry operation for a given host request, means for terminating the response to the host request if the count of retry operations exceeds a predetermined maximum and means for monitoring the response time that expires after an initial sequence begins and means for terminating the response to the host request if the response time exceeds a predetermined timeout interval.

55. A data storage facility as recited in claim 52 comprising means for generating request messages that identify a cache tag entry location and means for generating request messages that identify a cache memory location.

56. A data storage facility as recited in claim 52 wherein a host request is a host read request for transferring data from a specific data storage location, said data storage facility additionally comprising means for generating a first request message to obtain the status of a cache tag in the cache tag location corresponding to the address in the first common address space and means for generating a response message to indicate whether the located cache tag entry corresponds to the requested address and is unlocked.

57. A data storage facility as recited in claim 56 wherein the response message indicates that the located cache tag corresponds to the requested address and is unlocked, said data storage facility additionally comprising means for sending a second request message that initiates a transfer of the data in the specified cache memory location and means for generating a response message to the second request message with the data for the response to the host read request.

58. A data storage facility as recited in claim 56 wherein the response message fails to indicate that the located cache tag corresponds to the requested address and is unlocked, said data storage facility additionally comprising means for generating a second request message requesting the data to be transferred to the specified cache memory location from the corresponding data storage location and means for generating a response message with the data from the specified cache memory location.

59. A data storage facility as recited in claim 58 additionally comprising means for sending a third request message for unlocking the cache tag and means for generating a response message indicating the success of that operation.

60. A data storage facility as recited in claim 52 wherein a host request is a host write request with data for transfer to a specific data storage location, said data storage facility additionally comprising means for generating a first request message identifying two cache memory locations for receiving the data in the host write request and means for requesting the status of each cache tag and means for generating a response message indicating whether each of the located cache tags corresponds to the requested address and is locked for use in the specified transfer.

61. A data storage facility as recited in claim 60 wherein the response message indicates that the located cache tags correspond to the requested address and are locked for use in the specified transfer, said data storage facility additionally comprising means for sending a second request message to each of the cache memory locations identified by the cache tags with the data from the host request.

62. A data storage facility as recited in claim 61 additionally comprising means for sending a response message to the second request message indicating success and means for sending a third request message to unlock the cache tag.

63. A data storage facility as recited in claim 62 wherein the cache tag locations and cache memory locations are characterized by operating states including exclusive and modified-shared operating states indicating only one location in one cache memory location or two cache memory locations, respectively, contain data for one data storage location, said data storage facility additionally comprising means responsive to the third request message for updating the operating state to a modified-shared state and means for sending a response message.

64. A data storage facility as recited in claim 61 wherein the a plurality of data storage locations are to receive the data in the host write request, said data storage facility comprising means for sending a request message to lock the addressed cache tag, means for generating a response message indicating that success of that operation and means responsive to a response message indicating that the data has been written to all the data storage locations for terminating the correspondence between the cache tag and the data storage location in the first common address space.

65. A data storage facility as recited in claim 52 additionally comprising means for monitoring the utilization of the cache memory, means for selecting a cache memory location that can be made available for other data storage locations, means responsive to the selection for generating a first request message to lock the corresponding cache tag and means responsive to a response message indicating that success of that operation for terminating the correspondence between the cache tag and the data storage location in the first common address space.

66. A data storage facility with a first plurality of persistent data storage locations in a plurality of magnetic disk drives having addresses in a first common address space and having control logic for transferring data in response to host requests, said facility comprising:

A) a plurality of cache nodes comprising a second plurality of cache memory locations in another address space, each of said cache memory locations being adapted to store data,

B) a plurality of cache tag controller nodes comprising redundant cache tag locations for each of the second plurality of cache memory locations, each cache tag location adapted to store a cache tag with status information about a corresponding cache memory location, and

C) a control including;

i) a first address converter that converts an address in the data transfer request into an address in the first common address space,

ii) a second address converter that converts the address for the first common address space into an address for a cache tag location,

iii) a tester that determines the presence of a cache tag location that corresponds to the location in the host request, and

iv) a transfer control that transfers data with the corresponding cache memory location for predetermined values of the corresponding status information.

67. A data storage facility as recited in claim 66 additionally comprising means a message sequencer that generates a sequence of request messages for obtaining the status of a cache tag location and response messages with the requested status.

68. A data storage facility as recited in claim 67 additionally comprising means for a timer that defines a predetermined time internal during which a response message will be accepted and a control that restarts the sequencer when a response message is received after the predetermined timeout interval.

69. A data storage facility as recited in claim 67 additionally comprising means a retry counter that is modified curing each retry operation for a given host request, a control that terminates the response to the host request if the retry counter exceeds a predetermined maximum and a timer-based monitor that terminates the response to the host request if said monitor determines that the response time exceeds a predetermined timeout interval.

70. A data storage facility as recited in claim 67 comprising a request message generator in each I/O node for transmitting messages to the cache nodes and cache controller nodes means and a request message generator in each cache node for transmitting messages to the cache nodes.

71. A data storage facility as recited in claim 67 wherein a host request is a host read request for transferring data from a specific data storage location, said sequencer comprising a first request message generator that transmits a first request message to the said cache tag controller to obtain the status of a cache tag corresponding to the address in the first common address space and a first a response message generator that transmits a response message when the cache tag corresponds to the requested address and is unlocked.

72. A data storage facility as recited in claim 71 wherein said response message indicates that the located cache tag corresponds to the requested address and is unlocked, said I/O node including a second request message that transmits a request message to an identified cache node whereby the cache node initiates a transfer of the data in the specified cache memory location and a second response message generator in the cache node for transmitting a response message to the requesting I/O node with the data for the response to the host read request.

73. A data storage facility as recited in claim 71 wherein the response message fails to indicate that the located cache tag corresponds to the requested address and is unlocked, said data storage facility additionally comprising a second request message generator in each cache node that requests the data to be transferred to the specified cache memory location from the corresponding data storage location and a second response message generator in each cache node for transmitting a response message with the data from the specified cache memory location.

74. A data storage facility as recited in claim 73 additionally comprising a third request message generator in said I/O nodes that transmits a request message to the cache tag controller for unlocking the cache tag and a response message generator in each cache tag controller node for generating a message indicating the success of that operation.

75. A data storage facility as recited in claim 67 wherein a host request is a host write request with data for transfer to a specific data storage location, said data storage facility additionally comprising a first request message generator in each I/O node for identifying two cache memory locations for receiving the data in the host write request and a response message generator in each said cache tag controller for transmitting a response message to a cache node indicating whether each of the located cache tags corresponds to the requested address and is locked for use in the specified transfer.

76. A data storage facility as recited in claim 75 wherein the response message indicates that the located cache tags correspond to the requested address and are locked for use in the specified transfer, said data storage facility a additionally comprising a second request message generator in each said I/O node for transmitting a request message to cache nodes by the cache tags with the data from the host request.

77. A data storage facility as recited in claim 76 additionally comprising a second response generator in said cache tag controller transmitting a response message to the I/OI node indicating success and a third request message generator in the I/O node for transmitting a third request message to unlock the cache tag.

78. A data storage facility as recited in claim 77 wherein the cache tag locations and cache memory locations are characterized by operating states including exclusive and modified-shared operating states indicating only one location in one cache memory location or two cache memory locations, respectively, contain data for one data storage location, said data storage facility additionally comprising a third request message generator in each cache node for transmitting a third request message that updates the operating state to a modified-shared state and a response message generator in each cache tag controller for transmitting a response message.

79. A data storage facility as recited in claim 76 wherein the a plurality of data storage locations are to receive the data in the host write request, said data storage facility comprising a request message generator in each I/O node for generating a request message to lock the addressed cache tag, a response generator in each cache tag controller node for generating a response message indicating that success of that operation and a second request message generator in each cache node that responds to a response message indicating that the data has been written to all the data storage locations for terminating the correspondence between the cache tag and the data storage location in the first common address space.

80. A data storage facility as recited in claim 67 additionally comprising means for monitoring the utilization of the cache memory, means for selecting a cache memory location that can be made available for other data storage locations, means responsive to the selection for generating a first request message to lock the corresponding cache tag and a response message generator for transmitting a response message indicating the success of that operation thereby to terminate the correspondence between the cache tag and the data storage location in the first common address space.