Hitachi Dynamic Link Manager Software Users Guide for AIX (6.6) (T5208-96010, April 2011)

1. Overview of HDLM

1.2 HDLM Features

HDLM features include the following:

The ability to distribute a load across multiple paths. This is also known as load

balancing.

When a host is connected to a storage system via multiple paths, HDLM can

distribute the load across all the paths. This prevents one, loaded down path from

affecting the processing speed of the entire system.

For details on load balancing, see 2.6 Distributing a Load Using Load Balancing.

The ability to continue running operations between a host and storage system, even if

there is a failure. This is also known as performing a failover.

When a host is connected to a storage system via multiple paths, HDLM can

automatically switch to another path if there is some sort of failure in the path that

is currently being used. This allows operations to continue between a host and a

storage system.

For details on performing failovers, see 2.7 Performing Failovers and Failbacks

Using Path Switching.

The ability to bring a path that has recovered from an error back online. This is also

known as performing a failback.

If a path is recovered from an error, HDLM can bring that path back online. This

enables the maximum possible number of paths to always be available and online,

which in turn enables HDLM to better distribute the load across multiple paths.

Failbacks can be performed manually or automatically. In an automatic failback,

HDLM will automatically restore the path to an active state after the user has

corrected the problem that exists on the physical path.

For details on performing failbacks, see 2.7 Performing Failovers and Failbacks

Using Path Switching.

The ability to automatically check the status of any given path at regular intervals. This

is also known as path health checking.

HDLM can easily detect errors by checking the statuses of paths at user-defined

time intervals. This allows you to check for any existing path errors and to resolve

them promptly and efficiently.

For details on setting up and performing path health checking, see 2.9 Detecting

errors by using path health checking.