HP Hitachi Dynamic Link Manager Software - Manual (Page 48)

2. HDLM Functions
24
• 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 describes the features of the
load balancing algorithms.
Table 2-6: Features of the Load Balancing Algorithms
#
Some I/O operations managed by HDLM can be distributed across all, available
paths, and some cannot. Thus, you should be aware that even if you specify the
Round Robin algorithm, some of the I/O operations will never be issued
uniformly across all the given paths.
The default algorithm is the Extended Least I/Os algorithm, which is set when HDLM
is first installed. When an upgrade installation of HDLM is performed, the algorithm
that is currently being used is inherited.
Select the load balancing algorithm most suitable for the data access patterns of your
system environment. However, if there are no recognizable data access patterns, we
recommend using the default algorithm, the Extended Least I/Os algorithm.
You can specify the load balancing function by the
dlnkmgr
command's
set
operation. For details on the
set
operation, see 6.6 set (Sets Up the Operating
Environment).
Algorithm type Algorithm features
• Round Robin #
• Least I/Os
• Least Blocks
These types of algorithms are most effective when a lot of discontinuous,
non-sequential I/Os are issued.
• Extended Round Robin
• Extended Least I/Os
• Extended Least Blocks If the I/O data is from something like a read request and is generally sequential
with the previous I/Os, an improvement in reading speed can be expected due
to the storage system cache functionality. These types of algorithms are most
effective when a lot of continuous, sequential I/Os are issued.