Hitachi Dynamic Link Manager, User Manual, Page: 47 / 746

2. HDLM Functions
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Data When the Load Balancing Function Is Used , the load is balanced among the four
paths A, B, C, and D. If one of the paths were to become unusable, the load would be
balanced among the three, remaining 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 the path to use each time a certain number of I/Os are
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
was distributed will be used. However, if a specified number of I/Os has been
issued to a path, processing switches to the next path.
If the I/O is not sequential with the previous I/O, these algorithms select the path
to be used each time an I/O request is issued.