Multiplexing sends data from multiple sources to a single tape or disk device. This is useful if you have a tape or disk device that writes faster than a single system can send data, which (at this point) is just about every tape device.
Multiplexing does require tuning considerations with regards to restoration of the data. Generally speaking, the higher the multiplexing setting you use, the greater impact it can have on performance of an individual stream from within the set of multiplexed data. (If you're recovering all streams multiplexed together, MPX should have minimal impact on restore performance.) If NBU multiplexed several backups together, and you're only restoring one of them, it has to read all of the backups and throw away what it doesn't need. This reduces the overall effective throughput of the drive. If it reduces that speed to a speed slower than the bandwidth you have available for the restore, then it will slow you restore down.
Multistreaming establishes multiple connections, or threads, from a single system to the backup server. This is useful if you have a large system with multiple I/O devices and large amounts of data that need backing up.
Multistreaming also requires planning for implementation. To run effectively it needs to be able to get all needed resources at the same time to provide the shortest possible backup window. It also needs to be tested against the source storage to find the optimal number of streams that can be run. The more drives that are added will increase the backup speeds until the point where the source storage cannot provide the data any faster. At this point the backup times will start to increase because the storage is at 100% utilization.
The good news about Multistreaming is that it is able to shorten restore times for the same data. In general the destination storage will have a bottleneck at the writing of the data. With proper tuning of NUMBER_DATA_BUFFERS and SIZE_DATA_BUFFERS combined with fast tape and disk drives, restores in a Multistreaming configuration can approach a 1:1 ratio. This is a very good thing with respect to Disaster Recovery / Business Contingency.
