Method and apparatus for mirroring data in a remote data storage system

1. A method for transferring data from a data storage facility through an intersystem transfer path to a second, geographically remote facility wherein said data storage facility includes a data store for storing data in a retrievable form and interface means responsive to externally generated write requests for transferring data to the data store and wherein, during a normal operating mode, the interface means responds to a write request by causing a first transfer of the data from the interface means to the data store and a second transfer to the remote facility and processes a subsequent write request only if a prior write request has been successfully processed by the remote facility, said method comprising the additional steps of:

A) enabling an alternate operating mode and thereby disabling the normal operating mode, and

B) thereafter responding to each write request received at the interface means by causing a transfer of the data from the interface means to the data store and by initiating a transfer of the data to the remote facility whereby the data storage facility continues to process subsequent write requests even without a completion of processing of prior write requests by the remote facility, and

C) reverting the data storage facility to the normal operating mode when dynamic monitoring of data for which transfers have been initiated exceeds a maximum value.

2. A method as recited in claim 1 wherein each write request is a pending write request until processed and said dynamic monitoring obtains the number of pending write requests for transfers to the remote facility.

3. A method as recited in claim 2 wherein a host generates the write requests and the data storage facility interface means sends an acknowledgement that the write request to the remote facility has been processed upon receiving the write request during the alternate operating mode.

4. A method as recited in claim 3 wherein the interface means responds to each write request during the alternative operating mode by initiating the data transfer to the remote facility, by recording the existence of the pending write request and by clearing the recording when the remote facility indicates that the write request has been processed.

5. A method as recited in claim 1 wherein the data store is organized in logical volumes and tracks and includes means for indicating data for transfer to the remote facility on a track-by-track basis and wherein each write request is processed by setting track indicating means to a first state until the data in a track is processed by the remote facility whereupon the track indicating means is set to a second state, said dynamic monitoring determining the number of tracks in the first state.

6. A system as recited in claim 5 wherein a host generates the write requests and said data storage facility interface means includes means for sending an acknowledgement that the write request to said remote facility has been processed upon receiving the write request during the alternate operating mode.

7. A system as recited in claim 6 wherein said interface means responds to each write request during the alternative operating mode and includes means for initiating the data transfer to the remote facility, means for shifting the track indication for each track involved in the write request to the first state and means for clearing a track indication for each track for which said remote facility processes the data.

8. A method as recited in claim 5 wherein a host generates the write requests and the data storage facility interface means sends an acknowledgement that the write request to the remote facility has been processed upon receiving the write request during the alternate operating mode.

9. A method as recited in claim 8 wherein the interface means responds to each write request during the alternative operating mode by initiating the data transfer to the remote facility, by shifting the track indication for each track involved in the write request to the first state and by clearing a track indication for each track for which the remote facility processes the data.

10. A system for transferring data from a data storage facility through an intersystem transfer path to a second, geographically remote facility wherein said data storage facility includes a data store for storing data in a retrievable form and interface means responsive to externally generated write requests for transferring data to said data store and wherein, during a normal operating mode, a response to a write request transfers the data from said interface means to said first data storage facility and initiates a transfer to said remote facility and processes a subsequent write request only if a prior write request has been successfully processed by said remote facility, said system additionally comprising:

A) means for enabling an alternate operating mode thereby to disable the normal operating mode, and

B) means operative thereafter for responding to each write request received at said interface means by transferring the data from said interface means to said data store and by initiating a transfer of the data to said remote facility whereby said data storage facility continues to process subsequent write requests even without a completion of processing of prior write requests by said remote facility, and

C) dynamic monitoring means for reverting said data storage facility to the normal operating mode when dynamic monitoring of data for which transfers have been initiated exceeds a maximum value.

11. A system as recited in claim 10 wherein each write request is a pending write request until processed and said dynamic monitoring includes means for obtaining the number of pending write requests for transfers to said remote facility.

12. A system as recited in claim 11 wherein a host generates the write requests and said data storage facility interface means includes means for sending an acknowledgement that the write request to said remote facility has been processed upon receiving the write request during the alternate operating mode.

13. A system as recited in claim 12 wherein said interface means responds to each write request during the alternative operating mode and includes means for initiating the data transfer to the remote facility, means for recording the existence of the pending write request and means for clearing the recording when said remote facility indicates that the write request has been processed.

14. A system as recited in claim 10 wherein said data store is organized in logical volumes and tracks and includes means for indicating data for transfer to said remote facility on a track-by-track basis and wherein each write request is processed by setting track indicating means to a first state until the data in a track is processed by said remote facility whereupon said track indicating means is set to a second state, said dynamic monitoring means including means for determining the number of tracks in the first state.

15. A system for transferring data from a data storage facility through an intersystem transfer path to a second, geographically remote facility wherein said data storage facility includes a data store for storing data in a retrievable form and an interface responsive to externally generated write requests for transferring data to said data store and wherein, during a normal operating mode, a response to a write request transfers the data from said interface to said first data storage facility and initiates a transfer to said remote facility and processes a subsequent write request only if a prior write request has been successfully processed by said remote facility, said system additionally comprising:

A) a mode controller that enables an alternate operating mode and disables the normal operating mode, and

B) a dynamic monitoring control thereafter responding to each write request received at said interface by transferring the data from said interface to said data store and by initiating a transfer of the data to said remote facility whereby said data storage facility continues to process subsequent write requests even without a completion of processing of prior write requests by said remote facility, said mode controller reverting said data storage facility to the normal operating mode when said dynamic monitoring control determines that the data for which transfers have been initiated exceeds a maximum value.

16. A system as recited in claim 15 wherein each write request is a pending write request until processed and said dynamic monitoring control obtains the number of pending write requests for transfers to the remote facility.

17. A system as recited in claim 16 wherein a host generates the write requests and said interface sends an acknowledgement that the write request to the remote facility has been processed upon receiving the write request during the alternate operating mode.

18. A system as recited in claim 17 wherein said interface responds to each write request during the alternative operating mode and includes a data transfer control that initiates a data transfer to the remote facility, a recorder that records the existence of the pending write request and a recorder control that clears said recorder when said remote facility indicates that the write request has been processed.

19. A system as recited in claim 15 wherein said data store is organized in logical volumes and tracks and includes a track indicator that identifies tracks with data for transfer to said remote facility and wherein each write request is processed by setting said track indicator to a first state until the data in a track is processed by said remote facility whereupon said track indicator is set to a second state, said dynamic monitoring control determining the number of tracks in the first state.

20. A system as recited in claim 19 wherein a host generates the write requests and said interface sends an acknowledgement that the write request to said remote facility has been processed upon receiving the write request during the alternate operating mode.

21. A system as recited in claim 20 wherein said interface responds to each write request during the alternative operating mode and includes a data transfer control that initiates a data transfer to the remote facility, a recorder that shifts the track indication for each track involved in the write request to the first state and a recorder control that clears a track indication for each track for which said remote facility processes the write request.