Depending on the external storage type and system configuration, performance may not be improved when Extended Round-robin is set. In that case, Normal Round-robin is recommended.Supported external systems path mode for external volumes
“Single” or “Multi” path mode displays in Device Manager - Storage Navigator 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 I/O operations. This mode is recommended when the number of sequential I/O operations is large.
Disable: I/O operation is performed with only one path that is normal and has the highest priority. The same operation applies as that for Single path mode. When Disable is set for Load Balance Mode, load distribution is not performed. This mode is not recommended.
Depending on the external storage type and system configuration, performance may not be improved when Extended Round-robin is set. In that case, Normal Round-robin is recommended.