HP Hitachi Dynamic Link Manager Software - Manual (Page 43)

2. HDLM Functions
19
2.6 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.
Note:
Do not use the load balancing function that is accessible from the Microsoft iSCSI
Software Initiator user interface.
In a cluster environment, the load balancing function is available for the Thunder
9500V series, Lightning 9900 series, Lightning 9900V series, Hitachi AMS2000/
AMS/WMS/SMS series, Hitachi USP, Universal Storage Platform V/VM, and Virtual
Storage Platform. In a non-cluster environment, the load balancing function is
available for the Thunder 9500V series, Lightning 9900 series, Lightning 9900V
series, Hitachi AMS2000/AMS/WMS/SMS series, Hitachi USP, Universal Storage
Platform V/VM, Virtual Storage Platform, and EMC DMX series. For details on the
various cluster software that HDLM supports, see 2.14 Cluster Support.
Figure 2-7: Flow of I/O Data When the Load Balancing Function Is Not Used shows
the flow of I/O data when the load balancing function is not used. Figure 2-8: Flow
of I/O Data When the Load Balancing Function Is Used 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.