HiCommand Dynamic Link Manager (HDLM) for Windows Systems User's Guide (HIT5201-96001, January 2008)

20 Chapter 2 HDLM Functions
2.6 Load Distribution using Load Balancing
When the system contains multiple paths to an LU, HDLM can distribute the load across the
paths by using multiple paths for I/O. This functionality is called load balancing, and it
prevents a heavily loaded path from affecting the performance of the entire system.
Note that some I/O operations managed by HDLM can be distributed to each path, while
others cannot. Therefore, even when the load balancing function is used, I/O operations
may not be equally allocated to each path. For example, when Raid Manager issues IOCTL to
a command device, this I/O operation cannot be equally allocated to each path.
Note: Do not use the load balancing function set up in the Microsoft iSCSI Software Initiator
user interface.
In a cluster environment, the load balancing function is only available for TagmaStore,
Thunder 9200/9500V Series, Lightning 9900/9900V Series, and Universal Storage Platform V.
In a non-cluster environment, the load balancing function is available for TagmaStore,
Thunder 9200/9500V Series, Lightning 9900/9900V Series, Universal Storage Platform V, and
the EMC DMX series. For details on the cluster software supported by HDLM, see section
2.12.
Figure 2.7 shows the I/O flow when the load balancing function is not being used. Figure 2.8
shows the I/O flow when the load balancing function is being used. Both figures show an
example of an I/O operation being issued for the same LU from multiple applications.