Hitachi XP P9500 User Manual page 39

• 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.
Extended Round Robin
¢
The paths are simply 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 2-6 Features of the Load Balancing Algorithms on page 2-18
the features of the load balancing algorithms.
Hitachi Dynamic Link Manager User Guide (for Linux(R))
HDLM Functions
describes
2-17