multiplexing factor for tape from single source MA

Hello @Chinchilla 

The following goes over all of your Multiplexing questions and advanced understanding: 

https://documentation.commvault.com/2023e/expert/data_multiplexing_overview.html

To answer your questions directly, 

Q1 -

When a backup runs it will have stream ID’s for each stream run. This is the amount of streams we can use when we go ahead and read the data. Due to tape library being one writer multiplexing allows you to read multiple streams and write into one. So your “actual” multiplexing factor will be 5 IF you have 5 streams of data that needs to be copied. In short, it is a dynamic number from between 1-5 depending on how many stream ID’s need to be read at the same time. 

Q2 - If you increase your multiplexing factor, to do a restore you will have to read X times more data. 

For example if you are doing a 10GB restore and it was written to take with a multiplexing factor of 5. You will have to read from the tape 50GB and disregard 40GB of it to get your restore of 10. 

So if you increase your multiplexing factor from 5 to 10, you will have to read 100GB instead. 

The Benefit of having it set to 10 instead of 5 is that your performance will be faster if you have that amount of data to move. 

NOTE: A extremely high multiplexing factor can have huge impacts on restores. We never recommend above 8. 

Kind regards

Albert Williams