The following aspects of multiple data streams are adjustable:

• The total number of streams.

  The backup selection list determines the total number of streams that are started. The NEW_STREAM directive lets you configure a fixed number of streams, or you can allow the client dynamically define the streams.

  See Backup selections list directives for multiple data streams.

  Note:

  For best performance, use only one data stream to back up each physical device on the client. Multiple concurrent streams from a single physical device can adversely affect backup times. Backup times are affected because the device heads must move between the tracks that contain files for the respective streams.

• The number of streams that can run concurrently.

  The following factors determine the number of streams that can run concurrently for a policy or client:

  • Storage unit and schedule multiplexing limit.

    See Media multiplexing schedule attribute.

  • Number of the drives that are available.

  • Maximum concurrent jobs settings for the policy and client.

    Each storage unit and each schedule have a maximum multiplexing setting. The lower of the two settings is the limit for a specific schedule and storage unit. The maximum streams are limited to the sum of the multiplexing limits for all drives available in the storage unit and schedule combinations.

    For example, assume that two storage units have one drive in each. Multiplexing on storage unit 1 is set to 3 and multiplexing on storage unit 2 is set to 5. If multiplexing is set to 5 or greater in the schedules, then 8 streams can run concurrently.

The maximum jobs settings also limit the maximum number of streams as follows:

• Maximum jobs per client

  (Host Properties > Master Servers > Global Attributes).

  See Maximum jobs per client.

• Limit jobs per policy (policy attribute)

• Maximum data streams (Host Properties > Master Server > Client Attributes)..

  See Media multiplexing schedule attribute.

The maximum job settings are interdependent as follows:

• If the Maximum data streams option is not set, the limit is either Maximum jobs per client or Limit jobs per policy, whichever is lower.

• If the Maximum data streams option is set, NetBackup ignores Maximum jobs per client. Instead, NetBackup uses either Maximum data streams or Limit jobs per policy, whichever is lower.