HP XP Racks - Manual (Page 23)

NOTE: When you restore a path, use of the restored path is resumed.
Supported external systems path mode for external volumes
“Single” or “Multi” path mode displays in Remote Web Console for external volumes on the External
Path Group window. Path modes are based on the external storage system and cannot be changed.
In ALUA mode, all paths that are defined are used. I/O operation for external volumes is performed
through load balancing with the use of several paths (round-robin control). External paths connected
to ports in Passive status are not used.
Load Balance Mode
When the path mode of an external volume is Multi or ALUA, you can select an I/O control system
for the external storage system.
•
Depend on the selected external volume(s): If Enable is set for ALUA Settable on the external
volume, Normal Round-robin is set for Load Balance Mode automatically. If Disable is set for
ALUA Settable, Disable is set for Load Balance Mode automatically.
•
Normal Round-robin: Normal multi-path I/O control system. This distributes I/O to several
paths on which I/O operation is enabled for the external storage system. Specify this if
Extended Round-robin may lower I/O performance. This mode is recommended when the
number of sequential I/O operations is small.
•
Extended Round-robin: Extended multi-path I/O control system. I/O is distributed to several
paths on which I/O operation is enabled for the external storage system. For sequential I/O,
the external volume is divided into sections at regular intervals. In this case, the same path is
used for I/O within the same section which reduces the frequency of I/O distribution. Read
speed can be improved by using the cache function of the external storage system for sequential
Planning external paths and path groups 23