HP XP7 Storage - Manual (Page 26)

HDLM driver and NMP positions
The HDLM driver and NMP are positioned above the SCSI driver, causing each
application on a guest OS to access LUs in the storage system via the HDLM
driver and NMP.
The following figure shows the positioning of the HDLM driver and NMP.
Figure 2-6 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.
2-8
HDLM Functions
Hitachi Dynamic Link Manager (for VMware®) User Guide