Hitachi MK-96RD626-07 User Manual page 37

When an error occurs in the path that is being used for I/Os, the I/O
execution path is switched to the path with the second highest priority in
the Normal status. If there is no path in the Normal status other than the
path that is being used for I/Os, the status of the path in the Standby
status is automatically changed to Normal, and the I/O execution path is
switched to that path.
Note: Only when the external storage system is EVA storage system, as
you restore the path with the highest priority, the I/O execution path is
switched back to the restored highest priority path. In this case, the status
of the path for which the status has been changed to Normal when the
error has occurred is changed back to Standby.
Local Storage System
External
Port A
External
Internal
Volume Port B
External
Port C
Local Storage System
External
Port A
External
Internal
Volume Port B
External
Port C
Legend
: Internal volume where the external volume is mapped
: I/O
Figure 2-8 Single Mode with Alternate Paths in Normal and Standby
About Universal Volume Manager Operations
Hitachi Universal Storage Platform V/VM Universal Volume Manager User's Guide
External Storage System
Port
Path
Priority 1
WWN A
Status: Normal
Port
Path
Priority 2
WWN B
Status: Standby
Path
Port
Priority 3
WWN C
Status: Normal
External Storage System
Path
Port
Error
Priority 1
WWN A
Status: Blockade
Path
Port
Priority 2
WWN B
Status: Standby
Path
Port
Priority 3
WWN C
Status: Normal
External
Volume
External
Volume
2-17