What is the difference between multiplexing and multistreaming?

Multiplexing sends data from multiple clients to a single tape drive.
This is useful for low end clients with slow throughput (such as over a slow network connection). Since these clients cannot send data fast enough to keep the tape drive busy, multiplexing will allow backups of multiple clients to send data to a single tape drive simultaneously. Multiplexing is the process of alternately sending (interleaving) data. In this case, alternately writing or interleaving multiple clients data to a single tape.

Multistreaming sends data from a single client to multiple tape drives.
Multistreaming is on the other end of the spectrum where there is a high-end client and throughput that is greater than a tape drive can handle. Multistreaming allows multiple backups (streams) of a single client to occur simultaneously to multiple tape drives.

Multiplexing and multistreaming can be used together. The right combination can reduce backup times of large clients. Be aware that multiplexing will reduce the performance of restores. The larger the multiplexing factor, the greater the impact on restore performance.