Dell NetWorker 19.9 Administration Guide

Balancing the load on the storage node

The Save Session Distribution feature allows you to configure how NetWorker distributes save sessions between the storage nodes.

You can apply this feature to all NetWorker clients or to selected clients. This feature has two options:

• Max sessions—Distributes save sessions that are based on the setting in the Max sessions option in the storage node device resource. This is the default distribution method. The Max sessions option is more likely to concentrate the backup load on fewer storage nodes.
• Target sessions—Distributes save sessions that are based on the setting defined in the Target sessions option in each storage node device resource. The Target sessions option is more likely to spread the backup across multiple storage nodes.

When you select the Max sessions option, the NetWorker server distributes the save sessions for a client among eligible storage nodes as follows:

1. Identifies the available storage nodes in the NetWorker client’s storage node affinity list.
2. Uses an available device on the first storage node in the list that is working below its Target sessions level.
3. When all devices on the first storage node are running at their target sessions level but some are running below their max sessions level, then NetWorker uses the least loaded device.
4. Continues until all available devices on all storage nodes in the client’s storage node affinity list are in use.

When you select the Target sessions option, the NetWorker server distributes save sessions among eligible storage nodes as follows:

1. Identifies the available storage nodes in the storage node affinity list for the client.
2. Uses an available device on the first storage node in the list that is working below its Target sessions level.
3. When all devices on the first storage node are running at their target sessions levels, continue to the next storage node even if some devices are running below their max sessions level.
4. When all devices on all eligible storage nodes are running at their target sessions level, use the least loaded device that is running below its max session value.
5. Continues to send data to the least loaded device that is running below the max session value, until all devices on all available storage nodes are running at their max session levels.

Note the following performance considerations for storage node load balancing:

• Depending on the configuration of the backup environment, there is a potential to shorten the backup times by using the device Target sessions option rather than the device Max sessions option. However, using the device Target sessions option with the checkpoint restart feature can result in slower recovery times because a single save set is more likely to be spread across multiple storage nodes.
• It is recommended to use the default values for Max sessions as lowering these values can impact performance.
• Each NetWorker client has a storage node affinity list. The Save sessions distribution feature can only distribute a backup session for a client to multiple storage nodes when the client resource has two or more storage nodes in its storage node affinity list. The storage node affinity list is specified on the Globals (2 of 2) tab in the NetWorker Client Properties window.