MANAGING RESERVATION-CONTROL IN A STORAGE SYSTEM

1 . A method of managing reservation-control in a storage system that consists of a plurality of interfaces and a common storage resource, the method comprising:

responsive to receiving at an originator interface a reservation command related to the common storage resource, implementing a multi-phase reservation synchronization protocol including:

a lock phase consisting of:

locking the resource on a central controlling process,

backing up respective lock phase data on a backup control process, and

issuing a lock phase completion indication;

an execution phase consisting of:

executing locally on each one of the plurality of interfaces a reservation operation, and

issuing an execute phase completion indication; and

an unlock phase consisting of:

unlocking the resource on the central controlling process;

backing up respective unlock phase data on a backup control process, and

issuing an unlock phase completion indication.

2 . The method according to claim 1 , wherein said lock phase is initiated by the originator interface in response to receiving the reservation command, and said execution and unlock phases are initiated by the originator in response to receiving the lock phase completion and the execute phase completion indications, respectively.

3 . The method according to claim 1 , further comprising:

receiving at the originator interface the reservation command;

forwarding the reservation command to the central controlling process,

and wherein said multi-phase reservation synchronization protocol is initiated for the reservation command by the central controlling process, including initiating said lock phase, said execution phase and said unlock phase.

4 . The method according to claim 1 , wherein the execution phase includes receiving at the central controlling process an acknowledgment of the execution of the reservation operation on each one of the plurality of interfaces, and wherein said issuing an execute phase completion indication is responsive to said receiving at the central controlling process an acknowledgment of the execution of the reservation operation on each one of the plurality of interfaces.

5 . The method according to claim 3 , further comprising in case the central controlling process failed:

configuring the backup control process as a replacement controlling process;

implementing a takeover process including requesting each one of the plurality of interfaces to provide the replacement controlling process with any reservation phase command that was issued by the interface and for which no response was received from the central controlling process; and

processing responses from the plurality of interfaces using the back up phase data to determine a current phase of a reservation command.

6 . A storage system, comprising:

a plurality of interfaces;

a common storage resource;

a central controlling process; and

a backup controlling process,

wherein in response to receiving at an originator interface a reservation command related to the common storage resource, implementing a multi-phase reservation synchronization protocol including:

a lock phase consisting of:

locking the common storage resource on the central controlling process,

backing up lock phase data related to the lock on a backup control process, and

issuing a lock phase completion indication to the originator interface;

an execution phase consisting of:

executing locally on each one of the plurality of interfaces a reservation operation, and

issuing an execute phase completion indication to the originator interface; and

an unlock phase consisting of:

unlocking the resource on the central controlling process;

backing up respective unlock phase data on a backup control process, and

issuing an unlock phase completion indication to the originator.

7 . A program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform a method of managing reservation-control in a storage system that consists of a plurality of interfaces and a common storage resource, the method comprising:

responsive to receiving at an originator interface a reservation command related to the common storage resource implementing a multi-phase reservation synchronization protocol including:

a lock phase consisting of:

locking the resource on a central controlling process,

backing up respective lock phase data on a backup control process, and

issuing a lock phase completion indication;

an execution phase consisting of:

executing locally on each one of the plurality of interfaces a reservation operation, and

issuing an execute phase completion indication; and

an unlock phase consisting of:

unlocking the resource on the central controlling process;

backing up respective unlock phase data on a backup control process, and

issuing an unlock phase completion indication.