HP Hitachi Dynamic Link Manager Software User Manual

Page 42

2. HDLM Functions

(2) When Using the Lightning 9900 Series, Lightning 9900V Series, Hitachi USP,

Universal Storage Platform V/VM, Virtual Storage Platform, Hitachi AMS2000

Series, or Hitachi SMS

All online paths are owner paths. Therefore, for the example in Figure 2-6: Flow of

I/O Data When the Load Balancing Function Is Used, the load is balanced among the

four physical paths A, B, C, and D. If one of the physical paths were to become

unusable, the load would be balanced among the three, remaining physical paths.

2.7.2 Load Balancing Algorithms

HDLM has the following six load balancing algorithms:

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

The above algorithms are divided into two categories, which differ in their processing

method. The following describes both of these processing methods:
The Round Robin, Least I/Os, and Least Blocks algorithms

These algorithms select which path to use every time an I/O is issued. The path

that is used is determined by the following:

• Round Robin

The paths are simply selected in order from among all the connected paths.

• Least I/Os

The path that has the least number of I/Os being processed is selected from

among all the connected paths.

• Least Blocks

The path that has the least number of I/O blocks being processed is selected

from among all the connected paths.

The Extended Round Robin, Extended Least I/Os, and Extended Least Blocks

algorithms

These algorithms determine which path to allocate based on whether the I/O to be

issued is sequential with the immediately preceding I/O.
If the I/O is sequential with the previous I/O, the path to which the previous I/O