Note the following:

• Multiplexing

  To use multiplexing effectively, you must understand the implications of multiplexing on restore times. Multiplexing may decrease backup time for large numbers of clients over slow networks, but it does so at the cost of recovery time. Restores from multiplexed tapes must pass over all non-applicable data. This action increases restore times. When recovery is required, demultiplexing causes delays in the restore: NetBackup must search the tape to accomplish the restore.

  Restores should be tested to determine the impact of multiplexing on restore performance. Also, a smaller maximum fragment size when multiplexing may help restore performance.

  See Effect of fragment size on NetBackup restores.

  When you initially set up a new environment, keep the multiplexing factor low. A multiplexing factor of four or less does not highly affect the speed of restores, depending on the type of drive or system. If the backups do not finish within their assigned window, multiplexing can be increased to meet the window. However, a higher multiplexing factor provides diminishing returns as the number of multiplexing clients increases. The optimum multiplexing factor is the number of clients that are needed to keep the buffers full for a single tape drive.

  Set the multiplexing factor to four and do not multistream. Run benchmarks in this environment. Then you can begin to change the values until both the backup and restore window parameters are met.

• Multiple data streams

  The NEW_STREAM directive is useful for fine-tuning streams so that no disk subsystem is under-utilized or over-utilized.