Hitachi Dynamic Link Manager Software Users Guide for Linux

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Hitachi AMS2000 series
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Hitachi SMS series
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HUS100 series
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HUS VM
#: This storage system applies when the dynamic I/O path control
function is disabled.
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:
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Round Robin
The paths are simply selected in order from among all the connected
paths.
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Least I/Os
The path that has the least number of I/Os being processed is
selected from among all the connected paths.
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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.
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Extended Round Robin
HDLM Functions
2-17
Hitachi Dynamic Link Manager (for Linux®) User Guide