HP XP P9500 Storage - Manual (Page 25)

the ports of the external storage system) will be displayed in a dialog box when you map an
external volume. In this dialog box, you can set external paths by selecting the starting points and
the ending points of the paths according to the actual cable connections.
Setting of redundant external paths
You can set redundant external paths (add alternate paths) when you set the external paths. You
can also add an alternate path or change the priority after completing the mapping of the external
volume.
Path mode
Path mode is either Single mode or Multi mode, depending on the controller capability of the
external storage system.
NOTE: Single mode and Multi mode are based on the controller capability of the external device
and cannot be changed.
•
In the Single mode, only the path with the highest priority (primary path) is used to execute
the I/O to the external volume. When an error occurs in the primary path, the path with the
second highest priority is used.
•
In the Multi mode, all of the set paths are used at the same time. The multiple paths are used
to execute the I/Os to the external volume thus distributing the work load (round-robin
processing).
For example, when a volume in the external storage system with the path mode of the Single mode
is mapped as an internal volume using External Storage, the host I/O operations to the external
volume are enabled using the primary path set in the mapping operation. The path is automatically
switched to the alternate path when the primary path set in mapping operation cannot be used
due to, for instance, maintenance operation in the storage system, or a failure in the channel
processor. Because the path is switched to the alternate path, the I/O operation to the external
volume continues even though an error occurred in the original path.
NOTE: When the primary path cannot be used for three minutes continuously, the path is switched
to the alternate path.
Examples of alternate paths
Figure 10 (page 25) illustrates an example of setting an alternate path. External storage system
ports, “WWN A” and “WWN B,” are connected to “CL1-A” and “CL2-A,” respectively, which
are set to the external ports in the local storage system. For redundancy, specify the port of a
different cluster in the local storage system for the alternate path. Therefore, “CL1” port and “CL2”
port are specified.
Figure 10 Example of alternate path setting
Configuring External Storage 25