Hitachi MK-96RD626-07 - Manual (Page 37)

About Universal Volume Manager Operations 2-17
Hitachi Universal Storage Platform V/VM Universal Volume Manager User’s Guide
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.
External
Port B
Port
WWN B
Internal
Volume
External
Port A
Port
WWN A
External
Volume
External
Port C
Port
WWN C
External
Port B
Port
WWN B
Internal
Volume
External
Port A
Port
WWN A
External
Volume
External
Port C
Port
WWN C
Error
Path
Priority 1
Status: Normal
Path
Priority 1
Status: Blockade
Path
Priority 2
Status: Standby
Path
Priority 3
Status: Normal
Path
Priority 3
Status: Normal
Path
Priority 2
Status: Standby
: I/O
External Storage System
Legend
: Internal volume where the external volume is mapped
Local Storage System
External Storage System Local Storage System
Figure 2-8 Single Mode with Alternate Paths in Normal and Standby