HP Hitachi Dynamic Link Manager Software User Manual
Page 47
2. HDLM Functions
23
(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 2-8: Flow of
I/O 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.
2.6.2 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 data of
the I/O to be issued is sequential with the data of the I/O that was issued
immediately beforehand.