Dell NetWorker 19.9 Administration Guide

Client parallelism and parallel save streams

Client parallelism defines the number of data streams that a client can use simultaneously during backup.

Data streams include backup data streams, savefs processes, and probe jobs.

The default value is different for the NetWorker server than it is for all other client resources:

• For the NetWorker server client resource, the default value is 12. This higher default value enables the server to complete a larger number of index backups during a Server backup action.
• For all other clients, the default value is 4.

To define client parallelism, use the Parallelism attribute of the Client resource. You can find the parallelism attribute on the Globals(1 of 2) tab of the Client property dialog box, in the NetWorker Administration window.

The NetWorker for Network Data Management Protocol (NDMP) User Guide provides more information about recommended parallelism settings for NDMP clients.

To avoid disk contention for clients other than the NetWorker server, specify a value that is the same as or fewer than the number of physical disks on the client that are included in the backup.

For a Windows client with the ALL keyword save set attribute, the backup includes the local disks, for example C: and D: drives as well as the System State and System DB. In this example, you can keep the default parallelism setting of 4. If you define multiple save sets on the same disk, for example, C:\users, C:\system, C:\docs and so on , a higher client parallelism results in multiple save streams attempting to access the disk at the same time.

The NetWorker Performance Optimization Planning Guide provides more information about recommended client parallelism values and performance benefits.

Enabling the parallel save streams (PSS) feature for a Client resource allows you to back up each save set for the client by using multiple parallel save streams to one or more destination backup devices. You can use PSS to perform the scheduled file level backup of file systems, and block based backups.

You can use PSS for clients with supported UNIX, Linux, and Windows operating systems. Supported save sets for PSS include the Save Set ALL, and individual save points including Disaster_Recovery, deduplicated, and CSV volumes (Windows only). Checkpoint restart is not supported when you use PSS.

When you enable PSS, you can specify the maximum number of save streams that a client can send simultaneously for one or more save set backups concurrently running by using the Parallelism attribute in the Client Properties dialog. The default value for the Parallelism attribute is different for the NetWorker Server than it is for all other Client resources:

• For the NetWorker Server Client resource, the default value is 12. This higher default value enables the server to complete a larger number of index backups during a file system backup of the server or other index backups.
• For all other clients, the default value is 4.

Enabling PSS results in significant performance improvements due to save set aggregation, where the NetWorker Server starts a single save process per client with all client save sets that are passed to the single process for various processing optimizations, such as minimal Windows VSS snapshots and support for the following:

• Four parallel streams are started per save set, subject to any client parallelism limitations that might prevent all save sets from starting simultaneously.
• The ability to modify the number of parallel streams per save set by defining the new PSS:streams_per_ss environment variable save operations attribute in the properties of a Client resource. For example, setting PSS:streams_per_ss=2,* splits all save sets into two parallel save streams, whereas PSS:streams_per_ss=3,/data1, 5,/data2 splits /data1 into three parallel save streams and /data2 into five parallel save streams.
• Automatic stream reclaiming, which dynamically increases the number of active streams for an already running save set backup to maximize utilization of limited client parallelism conditions.

The NetWorker Performance Optimization Planning Guide provides complete details on PSS requirements and performance benefits.