HP XP P9500 Hitachi Dynamic Link Manager Software User Guide for VMWare (HIT52 - Page 24
Distributing a Load Using Load Balancing, Positioning of HDLM Driver and NMP
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Figure 2-4 Positioning of HDLM Driver and NMP Distributing a Load Using Load Balancing When the system contains multiple paths to a single LU, HDLM can distribute the load across the paths by using multiple paths to transfer the I/O data. This function is called load balancing, and it prevents a single, heavily loaded path from affecting the performance of the entire system. Note that some I/O operations managed by HDLM can be distributed across all, available paths, and some cannot. Therefore, even when the load balancing function is used, a particular I/O operation might not necessarily allocate data to every available path. RAID Manager issuing IOCTL to a command device is an example of an I/O operation that cannot allocate data to every path. Figure 2-5 Flow of I/O Data When the Load Balancing Function Is Not Used on page 2-7 shows the flow of I/O data when the load balancing function is not used. Figure 2-6 Flow of I/O Data When the Load Balancing Function Is Used on page 2-8 shows the flow of I/O data when the load balancing function is used. Both figures show examples of I/O operations being issued for the same LU by multiple applications. 2-6 HDLM Functions Hitachi Dynamic Link Manager User Guide (for VMware(R))