HiCommand Dynamic Link Manager User's Guide (for Windows(R))

2.6.2 Algorithms for Load Balancing

HDLM has the following two algorithms for load balancing:

Round robin
Round robin distributes all I/Os among multiple paths.

Extended round robin
Extended round robin distributes I/Os to paths depending on the type of the I/O, which can be either sequential access or random access. For sequential access, I/Os are issued to a single path. For random access, I/Os will be distributed to multiple paths.

Table 2-5 Algorithms for Load Balancing describes the types of load balancing (round robin and extended round robin) for each I/O operation type.

Table 2-5 Algorithms for Load Balancing

Algorithm For sequential access For random access

Round robin

After an I/O operation is issued to a path once or a certain number of times, the path is switched to the next path.

The storage subsystem cache might not be fully usable.

When multiple applications that request sequential access are run concurrently, we recommend that you use the round robin algorithm in order to distribute I/Os across multiple paths.^#

After an I/O operation is issued to a path once or a certain number of times, the path is switched to the next path.

Extended round robin

After an I/O operation is issued to a path a certain number of times in succession, the path is switched to the next path. If sequential access is switched to random access before an I/O operation is issued to a path a certain number of times, the path is switched to the next path when sequential access is switched to random access.

The storage subsystem cache can be used.

When you execute only a single application that requests sequential access, such as a batch job running at night, we recommend that you use the extended round robin algorithm.^#

After an I/O operation is issued to a path once or a certain number of times, the path is switched to the next path.

#

The recommended algorithm depends on the type of applications, and the operations policy.

You can specify the load balancing function from the Options window of the HDLM GUI or by the dlnkmgr command's set operation. For details on how to use the window components, see 4.2.8 Viewing or setting up the operating environment, or 6.3 Options window. For details on the set operation, see 7.6 set (Sets the operating environment).

Note

Some I/O operations managed by HDLM can be distributed across all paths, and some cannot. Thus, you should be aware that even when you use the load balancing function, I/O operations cannot always be allocated uniformly across all paths.

When using MSCS, depending on the micro-program of the storage subsystem, you may not be able to use the load balancing function. For more details, see Hardware Notes provided with HDLM.

Algorithm	For sequential access	For random access
Round robin	After an I/O operation is issued to a path once or a certain number of times, the path is switched to the next path. The storage subsystem cache might not be fully usable. When multiple applications that request sequential access are run concurrently, we recommend that you use the round robin algorithm in order to distribute I/Os across multiple paths.^#	After an I/O operation is issued to a path once or a certain number of times, the path is switched to the next path.
Extended round robin	After an I/O operation is issued to a path a certain number of times in succession, the path is switched to the next path. If sequential access is switched to random access before an I/O operation is issued to a path a certain number of times, the path is switched to the next path when sequential access is switched to random access. The storage subsystem cache can be used. When you execute only a single application that requests sequential access, such as a batch job running at night, we recommend that you use the extended round robin algorithm.^#	After an I/O operation is issued to a path once or a certain number of times, the path is switched to the next path.

[Contents][Back][Next]

[Trademarks]