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 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 data of the I/O to be issued is sequential with the data of the I/O that was issued immediately beforehand.
If the data is sequential, the path used will be the one to which the data of the I/O that was issued immediately beforehand was distributed. 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.
The following table lists and describes the features of the load balancing algorithms.
Algorithm type |
Algorithm features |
|---|---|
|
These types of algorithms are most effective when a lot of discontinuous, non-sequential I/Os are issued. |
|
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). |
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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 set (sets up the operating environment).