HP XP Racks User Manual
Page 35
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.
The following table lists and describes the features of the load balancing
algorithms.
Table 2-4 Features of the Load Balancing Algorithms
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 there is a read request for I/O data that is sequential with
the data of the I/O that was issued immediately beforehand,
an improvement in reading speed can be expected due to the
storage system cache functionality. These types of
algorithms are most effective when many continuous I/Os
are issued (the I/O data is sequential).
#
Some I/O operations managed by HDLM can be distributed across all
paths, and some cannot. Thus, you should be aware that even if you
specify the Round Robin algorithm, I/O operations cannot always be
allocated uniformly across all paths.
By default, the Extended Least I/Os algorithm is set when HDLM is first
installed. When an upgrade installation of HDLM is performed, the existing
setting is inherited.
Select the load balancing algorithm most suitable for the data access patterns
in your system environment. If there are no recognizable data access
patterns, we recommend applying 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
HDLM Functions
2-13
Hitachi Dynamic Link Manager (for AIX) User Guide