Media multiplexing (schedule attribute)

The Media multiplexing attribute specifies the maximum number of jobs from the schedule that NetBackup can multiplex onto any one drive. Multiplexing sends concurrent backup jobs from one or several clients to a single drive and multiplexes the backups onto the media.

Specify a number from 1 through 32, where 1 specifies no multiplexing. Any changes take effect the next time a schedule runs.

Note:

Some policy types and some schedule types do not support media multiplexing. The option cannot be selected in those instances.

Caution:

For MS-SQL-Server policies, do not enable multiplexing for a schedule that is also configured to backup with multiple stripes. Restores fail when multiplexing is enabled for a schedule that uses more than one stripe.

To configure multiplexed backups, multiplexing must be indicated in both the storage unit (Maximum Streams Per Drive setting) and the schedule (Media Multiplexing setting) configuration. Regardless of the Media multiplexing setting, the maximum jobs that NetBackup starts never exceeds the Maximum Streams Per Drive value for the storage unit.

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.

Figure: Multiplexed backups shows the multiplexed flow of client data to a server.

Figure: Multiplexed backups

About multiplexing

Multiplexing is generally used to reduce the amount of time that is required to complete backups. The following table describes circumstances where performance improves by using multiplexing:

Table: Circumstances where multiplexing improves performance

Item	Description
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 effect of multiplexing on restore times, set the storage unit maximum fragment size to a value smaller than the largest allowed value. Also, on UNIX, enable fast-tape positioning (locate block), if it applies to the tape drives in use.

Consider the following configuration settings when using multiplexing.

Table: Properties and attributes that affect multiplexing

Item	Description	Where to find it
Limit jobs per policy (policy attribute)	Limits the number of jobs that NetBackup performs concurrently when a policy is run. Set this attribute high enough to support the specified level of multiplexing. See Limit jobs per policy (policy attribute).	In the NetBackup Administration Console, expand NetBackup Management > Policies. In the middle pane, double-click the Attributes node of a policy. Or, create a new policy and select the Attributes tab.
Maximum jobs per client (host property)	Limits the number of backup jobs that can run concurrently on any NetBackup client. This property is part of Global Attributes host properties. See Global attributes properties. 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, NetBackup cannot use the storage unit's full multiplexing capabilities. Select 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. To estimate the potential load that multiplexing can place on the central processing unit, consider the following limits: 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. See Maximum streams per drive storage unit setting.	In the NetBackup Administration Console, expand NetBackup Management > Host Properties > Primary Servers. In the right pane, double-click a primary server. In the Primary Server Properties dialog box, select Global Attributes from the left pane. The property appears in the right pane.
Maximum data streams (host property)	Set the maximum number of jobs that are allowed on a specific client without affecting other clients. This property is part of Client Attributes host properties. See General tab of the Client attributes properties.	In the NetBackup Administration Console, expand NetBackup Management > Host Properties > Primary Servers. In the right pane, double-click a primary server. In the Primary Server Properties dialog box, select Client Attributes from the left pane. The property appears in the right pane on the General tab.
Delay on multiplexed restores (host 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. This property is part of General Server host properties. See General tab of the Client attributes properties.	In the NetBackup Administration Console, expand NetBackup Management > Host Properties > Primary Servers. In the right pane, double-click a primary server. In the Primary Server Properties dialog box, select General Server from the left pane. The property appears in the right pane.
Media Multiplexing (policy schedule attribute)	If the limit is reached for a drive, NetBackup sends jobs to other drives. When NetBackup multiplexes jobs, it continues to add jobs to a drive until the number of jobs on the drive matches the Media Multiplexing limit or the Maximum streams per drive limit. See Media multiplexing (schedule attribute).	In the NetBackup Administration Console, expand NetBackup Management > Policies. In the middle pane, double-click the Schedules node of a policy. Or, create a new policy and select the Schedules tab. Click New to create a new schedule and configure the Media Multiplexing option.
Maximum streams per drive (storage unit setting)	NetBackup can add jobs from more than one schedule to a drive. When NetBackup multiplexes jobs, it continues to add jobs to a drive until the number of jobs on the drive matches the Maximum streams per drive limit or the Media Multiplexing limit. See Maximum streams per drive storage unit setting.	In the NetBackup Administration Console, expand NetBackup Management > Storage. In the left pane, click Storage Units. In the right pane, double-click a storage unit name. Or, create a new storage unit. The setting appears on the dialog box that appears.

Media multiplexing (schedule attribute)

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