HP XP External Storage Software - Manual (Page 28)

Figure 3 Example of alternate path configuration using two switches
In Figure 4 , two paths are configured between the internal LDEV and external LU. However, only one
port is specified in the local array and two ports are specified in the external arrays via the switch.
Since two ports of different clusters must be set in the local array for External Storage XP to use alternate
path settings, HP does not recommend the configuration shown in
Figure 4 .
Figure 4 Example of incorrect alternate path configurations
Examples of switching I/O execution paths to alternate paths
There are two alternate path modes: Single mode and Multi mode. This section describes examples
of the performance when the I/O execution path switches to the alternate path for each path mode.
For more information about path status, see Adding alternate paths by selecting multiple external LUs
(Add Paths) .
• Alternate path mode is Multi mode
Figure 5 shows an example of when the alternate path mode is Multi mode. When an error occurs
in one path, I/Os execute using paths other than the error path.
NOTE:
As you restore the error path, use of the restored path automatically resumes.
Preparing for External Storage XP operations 28