HP Hitachi Dynamic Link Manager Software User Manual

Page 42

2. HDLM Functions

Table 2-4: Features of the Load Balancing Algorithms

Some I/O operations managed by HDLM can be distributed across all paths, and

some cannot. Thus, you should be aware that even if you specify the Round Robin

algorithm, I/O operations cannot always be allocated uniformly across all paths.

By default, the Extended Least I/Os algorithm is set when HDLM is first installed.

When an upgrade installation of HDLM is performed, the existing setting is inherited.
Select the load balancing algorithm most suitable for the data access patterns in your

system environment. If there are no recognizable data access patterns, we recommend

applying the Extended Least I/Os algorithm.
You can specify the load balancing function by the

dlnkmgr

command's

set

operation. For details on the

set

operation, see 6.6 set (Sets Up the Operating

Environment).

Algorithm type

Algorithm features

• Round Robin

• Least I/Os
• Least Blocks

These types of algorithms are most effective when a lot of discontinuous,

non-sequential I/Os are issued.

• Extended Round Robin
• Extended Least I/Os
• Extended Least Blocks

If there is a read request for I/O data that is sequential with the data of the I/O

that was issued immediately beforehand, an improvement in reading speed can

be expected due to the storage system cache functionality. These types of
algorithms are most effective when many continuous I/Os are issued (the I/O

data is sequential).