Expander to control multipaths in a storage network

Abstract

A device is provided including a first SAS expander coupling a SAS initiator and the first port of a SAS target and a second SAS expander coupling the SAS initiator and the second port of the SAS target. The first SAS expander notifies the SAS initiator of a virtual expander address instead of its SAS address and notifies the SAS initiator of a virtual target port address instead of a SAS address of the first port. The second SAS expander notifies the SAS initiator of the virtual expander address instead of its SAS address, and notifies the SAS initiator of the virtual target port address instead of a SAS address of the second port such that the SAS initiator recognizes a single SAS expander coupled to a wide port of the SAS initiator and that the SAS target is connected to the single SAS expander through a single port.

1 . A system for controlling a multipath in a Serial Attached SCSI (SAS) network, comprising:
 a SAS initiator;   a SAS target including a first port and a second port;   a first SAS expander that forms a first path coupling the SAS initiator and the first port of the SAS target together; and   a second SAS expander that forms a second path coupling the SAS initiator and the second port of the SAS target together, wherein
 the first SAS expander notifies the SAS initiator of a virtual expander address instead of its own SAS address, the virtual expander address being a virtual SAS address owned in common by the first SAS expander and the second SAS expander, and notifies the SAS initiator of a virtual target port address, at least instead of a SAS address of the first port of the SAS target, the virtual target port address being a SAS address of a virtual port of the SAS target, 
 the second SAS expander notifies the SAS initiator of the virtual expander address instead of its own SAS address, and notifies the SAS initiator of the virtual target port address, at least instead of a SAS address of the second port of the SAS target, and 
 the SAS initiator recognizes that a single SAS expander is connected to a wide port of the SAS initiator itself, when being notified of the virtual expander address by the first SAS expander and the second SAS expander, and recognizes that the SAS target is connected to the single SAS expander through a port, when being notified of the virtual target port address by the first SAS expander and the second SAS expander. 
   
     
     
         2 . The system according to  claim 1 , wherein upon receipt of data having the virtual target port address as a destination address, each of the first SAS expander and the second SAS expander transmits the data to the SAS target by using as the destination address a SAS address of a currently used one of the first port and the second port, and associated with the virtual target port address. 
     
     
         3 . The system according to  claim 2 , wherein upon detection of a failure on a path to a specific one of the first port and the second port, each of the first SAS expander and the second SAS expander changes the SAS address of the currently used one of the first port and the second port and associated with the virtual target port address to the SAS address of an alternate one of the first port and the second port which is other than the specific one of the first port and the second port. 
     
     
         4 . A device that functions as a SAS expander coupling a SAS initiator and a SAS target together, comprising:
 a first notification unit to perform a process comprising:
 causing the SAS initiator to recognize a configuration where the device and a different device serving as SAS expanders are connected to the SAS initiator as a configuration where a single device serving as a SAS expander is connected to a wide port of the SAS initiator, and 
 notifying the SAS initiator of a virtual expander address instead of a SAS address of the device, the virtual expander address being a virtual SAS address owned in common by the device and the different device; and 
   a second notification unit to perform a process comprising:
 causing the SAS initiator to recognize a configuration where a first port of the SAS target is connected to the device and a second port of the SAS target is connected to the different device as a configuration where a port of the SAS target is connected to the single device, and 
 notifying the SAS initiator of a virtual target port address, at least instead of a SAS address of a first port of the SAS target, the virtual target port address being a SAS address of a virtual port of the SAS target. 
   
     
     
         5 . The device according to  claim 4 , further comprising:
 a storage unit to store association information which indicates an association between the virtual target port address and a SAS address of a currently used one of the first port and the second port;   a receiver to receive data having the virtual target port address as a destination address from the SAS initiator;   a determination unit to determine, as the destination address of data received by the receiver, the SAS address of the currently used one of the first port and the second port; and   a transmitter to transmit data received by the receiver to the SAS address of the currently used one of the first port and the second port as determined by the determination unit.   
     
     
         6 . The device according to  claim 5 , further comprising:
 a detection unit to detect a failure on a path to a specific one of the first port and the second port; and   a change unit to change the association information to indicate an association between the virtual target port address and an alternate one of the first port and the second port which is other than the specific one of the first port and the second port upon detection of the failure on the path to the specific one of the first port and the second port by the detection unit.   
     
     
         7 . A device that serves as a SAS expander coupling a SAS initiator and a SAS target together, comprising:
 a first notification unit to perform a process comprising:
 causing the SAS initiator to recognize a configuration where the device and a different device serving as SAS expanders are connected to the SAS initiator as a configuration where a single device serving as a SAS expander is connected to a wide port of the SAS initiator, and 
 notifying the SAS initiator of a virtual expander address instead of a SAS address of the device, the virtual expander address being a virtual SAS address owned in common by the device and the different device; 
   a second notification unit to perform a process comprising:
 causing the SAS initiator to recognize a configuration where a first port of the SAS target is connected to the device and a second port of the SAS target is connected to the different device as a configuration where a port of the SAS target is connected to the single device, and 
 notifying the SAS initiator of a virtual target port address, at least instead of a SAS address of a first port of the SAS target, the virtual target port address being a SAS address of a virtual port of the SAS target; 
   a storage unit to store association information which indicates an association between the SAS address of the first port, a SAS address of the second port, the virtual target port address, a SAS address of a priority port which is one of the first port and the second port, and a SAS address of a currently used one of the first port and the second port;   a detection unit to detect a failure on a path to a specific one of the first port and the second port;   a setting unit to set the association information to indicate,
 the SAS address of the priority port as the SAS address of the currently used one of the first port and the second port if no failure is detected by the detection unit on the path to the specific one of the first port and the second port, and 
 a SAS address of an alternate one of the first port and the second port which is other than the specific one of the first port and the second port as the SAS address of the currently used one of the first port and the second port if a failure is detected by the detection unit on the path to the specific one of the first port and the second port; 
   a receiver to receive data having the virtual target port address as a destination address from the SAS initiator;   a determination unit to determine, as the destination address of the data received by the receiver, the SAS address of the currently used one of the first port and the second port; and   a transmitter to transmit data received by the receiver to the SAS address of the currently used one of the first port and the second port as determined by the determination unit.   
     
     
         8 . A method for controlling a multipath in a SAS network including a SAS initiator, a SAS target, a first SAS expander and a second SAS expander, the method comprising:
 forming, by the first SAS expander, a first path coupling the SAS initiator and a first port of the SAS target together;   notifying, by the first SAS expander, the SAS initiator of a virtual expander address instead of a SAS address of the first SAS expander, the virtual expander address being a virtual SAS address owned in common by the first SAS expander and the second SAS expander;   notifying, by the first SAS expander, the SAS initiator of a virtual target port address, at least instead of a SAS address of the first port of the SAS target, the virtual target port address being a SAS address of a virtual port of the SAS target;   forming, by the second SAS expander, a second path coupling the SAS initiator and a second port of the SAS target together;   notifying, by the second SAS expander, the SAS initiator of the virtual expander address instead of a SAS address of the second SAS expander;   notifying, by the second SAS expander, the SAS initiator of the virtual target port address, at least instead of a SAS address of the second port of the SAS target such that the SAS initiator recognizes that a single SAS expander is connected to a wide port of the SAS initiator and further that the SAS target is connected to the single SAS expander through a single port.   
     
     
         9 . A computer program product for controlling a multipath in a SAS network including a SAS initiator, a SAS target, a first SAS expander and a second SAS expander, the computer program product comprising:
 a computer readable storage medium having computer readable program code embodied therewith, which when executed, causes a computer to perform a method comprising:
 forming, by the first SAS expander, a first path coupling the SAS initiator and a first port of the SAS target together; 
 notifying, by the first SAS expander, the SAS initiator of a virtual expander address instead of a SAS address of the first SAS expander, the virtual expander address being a virtual SAS address owned in common by the first SAS expander and the second SAS expander; 
 notifying, by the first SAS expander, the SAS initiator of a virtual target port address, at least instead of a SAS address of the first port of the SAS target, the virtual target port address being a SAS address of a virtual port of the SAS target; 
 forming, by the second SAS expander, a second path coupling the SAS initiator and a second port of the SAS target together; 
 notifying, by the second SAS expander, the SAS initiator of the virtual expander address instead of a SAS address of the second SAS expander; 
 notifying, by the second SAS expander, the SAS initiator of the virtual target port address, at least instead of a SAS address of the second port of the SAS target such that the SAS initiator recognizes that a single SAS expander is connected to a wide port of the SAS initiator and further that the SAS target is connected to the single SAS expander through a single port.