HiCommand Dynamic Link Manager User's Guide (for Windows(R))

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 that is set up in the Microsoft iSCSI Software Initiator user interface.

In a cluster environment, the load balancing function is only available for Thunder 9200/9500V Series, Lightning 9900/9900V Series, TagmaStore, and Universal Storage Platform V. In a non-cluster environment, the load balancing function is available for Thunder 9200/9500V Series, Lightning 9900/9900V Series, TagmaStore, Universal Storage Platform V, and the EMC DMX series. For details on the cluster software supported by HDLM, see 2.12 Cluster support.

Figure 2-7 I/O flow when the load balancing function is not being used shows the I/O flow when the load balancing function is not being used. Figure 2-8 I/O flow when the load balancing function is being used 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.

Figure 2-7 I/O flow when the load balancing function is not being used

When the load balancing function is not being used, I/O operations converge on one path (A). The load on the path (A) will cause a bottleneck, which might cause deterioration of the whole system's performance.

Figure 2-8 I/O flow when the load balancing function is being used

When the load balancing function is being used, I/O operations are distributed via paths (A), (B), (C), and (D). This prevents deterioration of the whole system's performance from a bottleneck on one path.

Organization of this section

2.6.1 Paths to which load balancing is applied

2.6.2 Algorithms for Load Balancing

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