About multiplexing

NetBackup multiplexing sends concurrent backups from one or several clients to a single storage device. NetBackup multiplexes the backups sequentially onto the media. Multiplexed and unmultiplexed backups can reside on the same volume. Separate volume pools or media IDs are not necessary.

Multiplexing is generally used to reduce the amount of time that is required to complete backups. The performance in the following situations is improved by using multiplexing:

Slow clients	Instances in which NetBackup uses software compression, which normally reduces client performance, are also improved.
Multiple slow networks	The parallel data streams take advantage of whatever network capacity is available.
Many short backups (for example, incremental backups)	In addition to providing parallel data streams, multiplexing reduces the time each job waits for a device to become available. Therefore, the storage device transfer rate is maximized.

No special action is required to restore a multiplexed backup. NetBackup finds the media and restores the requested backup. Multiplexing reduces performance on restores because it uses extra time to read the images.

To reduce the affect of multiplexing on restore times, set the storage unit maximum fragment size to a value smaller than the largest allowed value.

When NetBackup multiplexes jobs, it continues to add jobs to a drive until the number of jobs on the drive matches either of the following:

This schedule's Media Multiplexing setting

If the limit is reached for a drive, NetBackup sends jobs to other drives.
The storage unit's Maximum streams per drive setting

NetBackup can add jobs from more than one schedule to a drive.

See Maximum streams per drive setting.

Consider the following configuration settings when using multiplexing:

Limit jobs per policy	Set Limit jobs per policy high enough to support the specified level of multiplexing.
Maximum jobs per client	The Maximum Jobs Per Client property limits the number of backup jobs that can run concurrently on any NetBackup client. Maximum Jobs Per Client appears on the Global properties dialog box. Usually, the client setting does not affect multiplexing. However, consider a case where jobs from different schedules on the same client go to the same storage unit. In this case, the maximum number of jobs that are permitted on the client is reached before the multiplexing limit is reached for the storage unit. When the maximum number of jobs on the client is reached, it prevents NetBackup from fully using the storage unit's multiplexing capabilities. Choose a value that is based on the ability of the central processing unit to handle parallel jobs. Because extra buffers are required, memory is also important. If the server cannot perform other tasks or runs out of memory or processes, reduce the Maximum Streams Per Drive setting for the storage unit. Consider the following items to estimate the potential load that multiplexing can place on the central processing unit: The maximum concurrent jobs that NetBackup can attempt equals the sum of the concurrent backup jobs that can run on all storage units. The maximum concurrent jobs that can run on a storage unit equals the value of Maximum Streams Per Drive, multiplied by the number of drives.
Maximum jobs this client	You can set the maximum number of jobs that are allowed on a specific client without affecting other clients.
MPX restore delay	The Delay On Multiplexed Restores property applies to multiplexed restores. The property specifies how long the server waits for additional restore requests of files and raw partitions in a set of multiplexed images on the same tape. Delay On Multiplexed Restores appears on the General Server properties dialog box.