Unit attention processing in proxy and owner storage systems

1. An owner storage system, comprising:

a storage device configured to store a logical volume mapped between a host computer and a computer having multiple initiator ports; and

a processor configured:

to detect a unit attention condition for the logical volume,

to generate a unit attention code and a respective unique serial number in response to detecting the unit attention condition,

upon receiving an input/output (I/O) request for the logical volume from a given initiator port, to convey, to the given initiator port, the unit attention code and the respective unique serial number in response to the I/O request, and

upon determining, based on the unique serial number, that the processor has previously conveyed the unit attention code to any of the multiple initiator ports, to reconvey the I/O request, receive a response for the I/O request, and convey the result to the host computer.

2. The owner storage system according to claim 1 , wherein the unit attention condition is selected from a list comprising a management operation on the logical volume and a host request for the logical volume.

3. The owner storage system according to claim 2 wherein the management operation is selected from a list comprising resizing the logical volume, setting the logical volume to a read-only status and setting the logical volume to a read-write status.

4. The owner storage system according to claim 2 , wherein the host request is selected from a list comprising a request to release a reservation on the logical volume and a request to preempt a reservation on the logical volume.

5. The owner storage system according to claim 1 , wherein the I/O request is selected from a list comprising a request to read data from the logical volume and a request to write data to the logical volume.

6. The owner storage system according to claim 1 , wherein the computer comprises a proxy storage system, and wherein the logical volume comprises regions on the owner storage system that have a mapping between a host computer and the proxy storage system.

7. The owner storage system according to claim 1 , wherein the I/O request for the logical volume comprises a first I/O request for the logical volume, and comprising receiving a second I/O request for the logical volume from the given initiator port, performing the second I/O request, and conveying a result of the I/O request to the given initiator port.

8. A method comprising,

receiving, by a first computer, a input/output (I/O) request for a logical volume stored on an owner module, the I/O request being received from a given one of multiple initiator ports on a second computer;

conveying the I/O request to a third computer;

receiving, in response to the conveyed I/O request, a unit attention code and a respective unique serial number from the third computer;

upon determining, based on the unique serial number, that the first computer has not yet conveyed the unit attention code to any of the multiple initiator ports, conveying a unit attention message to the given initiator port; and

upon determining, based on the unique serial number, that the first computer has previously conveyed the unit attention code to any of the multiple initiator ports, reconveying the I/O request to the third computer, receiving a response for the I/O request from the third computer, and conveying the result to the second computer.

9. The method according to claim 8 , wherein the first computer comprises a proxy module, and wherein the second computer comprises a host computer, and wherein the third computer comprises the owner module, and wherein the unit attention message comprises the unit attention code.

10. The method according to claim 8 , wherein the first computer comprises a receiver module, and wherein the second computer comprises a host computer, and wherein the third computer comprises a sender module, and wherein the unit attention message comprises the unit attention code.

11. The method according to claim 8 , wherein the first computer comprises a sender module, and wherein the second computer comprises a receiver module, and wherein the third computer comprises the owner module, and wherein the unit attention message comprises the unit attention code and the respective unique serial number.

12. The method according to claim 8 , wherein the unit attention code indicates a management operation selected from a list comprising resizing the logical volume, setting the logical volume to read-only and setting the logical volume to read-write.

13. The method according to claim 8 , wherein the unit attention code indicates a host request selected from a list comprising a request to release a reservation on the logical volume and a request to pre-empt a reservation on the logical volume.

14. A storage facility, comprising:

a storage area network (SAN); and

first, second and third computers configured on the SAN, the first computer being coupled to the SAN via multiple ports and configured:

to receive, via a given one of the multiple ports, an input/output (I/O) request for a logical volume stored on an owner module, the I/O request being received from a given one of multiple initiator ports on the second computer,

to convey the I/O request to the third computer,

to receive, in response to the conveyed I/O request, a unit attention code and a respective unique serial number from the third computer,

upon determining, based the unique serial number, that the first computer has not yet conveyed the unit attention code to any of the multiple initiator ports, to convey a unit attention message to the given initiator port, and

upon determining, based on the unique serial number, that the first computer has previously conveyed the unit attention code to any of the multiple initiator ports, to reconvey the I/O request to the third computer, to receive a response for the I/O request from the third computer, and to convey the result to the second computer.

15. The storage facility according to claim 14 , wherein the first computer comprises a proxy module, and wherein the second computer comprises a host computer, and wherein the third computer comprises the owner module, and wherein the unit attention message comprises the unit attention code.

16. The storage facility according to claim 14 , wherein the first computer comprises a receiver module, and wherein the second computer comprises a host computer, and wherein the third computer comprises a sender module, and wherein the unit attention message comprises the unit attention code.

17. The storage facility according to claim 14 , wherein the first computer comprises a sender module, and wherein the second computer comprises a receiver module, and wherein the third computer comprises the owner module, and wherein the unit attention message comprises the unit attention code and the respective unique serial number.

18. The storage facility according to claim 14 , wherein the unit attention code indicates a management operation selected from a list comprising resizing the logical volume, setting the logical volume to read-only and setting the logical volume to read-write.