The following items describe the reasons to use multiple data streams:

• To reduce backup time

  Multiple data streams can reduce the backup time for large backups by splitting the backup into multiple streams. Use multiplexing, multiple drives, or a combination of the two to process the streams concurrently.

  Configure the backup so each device on the client is backed up by a separate data stream that runs concurrently with streams from other devices.

  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. The heads must move back and forth between the tracks that contain files for the respective streams.

  Figure: Multiple stream recommendations shows that multiple concurrent streams from a single device are not recommended.

• To reduce retry time for backup failures

  Because the backup streams run independently, the use of multiple data streams can shorten the retry time in the event of a backup failure. A single failure only terminates a single stream. NetBackup can restart the failed stream without restarting the others.

  For example, assume the backup for a 10-gigabyte partition is split into five streams, each containing 2 gigabytes. If the last stream fails after it writes 1.9 gigabytes (a total of 9.9 gigabytes is backed up), NetBackup retries only the last gigabyte stream. If the 10-gigabyte partition is backed up without multiple data streams and a failure occurs, the entire 10-gigabyte backup must be retried.

  The Schedule backup attempts property in the Global Attributes properties, applies to each stream. For example, if the Schedule backup attempts property is set to 3, NetBackup retries each stream a maximum of three times.

  The Activity Monitor displays each stream as a separate job. Use the job details view to determine the files that are backed up by each of these jobs.

  See Global Attributes properties .

• To reduce administration by running more backups with fewer policies

  Use multiple data streams in a configuration that contains large file servers with many file systems and volumes. Multiple data streams provide more backups with fewer policies than are otherwise required.