Hitachi Dynamic Link Manager Software Users Guide for AIX (6.6) (T5208-96010, April 2011)

2. HDLM Functions
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• 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 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 data of
the I/O to be issued is sequential with the data of the I/O that was issued
immediately beforehand.
If the data is sequential, the path used will be the one to which the data of the I/O
that was issued immediately beforehand was distributed. However, if a specified
number of I/Os has been issued to a path, processing switches to the next path.
If the data is not sequential, these algorithms select the path to be used each time
an I/O request is issued.
• Extended Round Robin
The paths are simply is selected in order from among all the connected paths.
• Extended Least I/Os
The path that has the least number of I/Os being processed is selected from
among all the connected paths.
• Extended Least Blocks
The path that has the least number of I/O blocks being processed is selected
from among all the connected paths.
Table 2-4: Features of the Load Balancing Algorithms describes the features of the
load balancing algorithms.