Best practices for Multiplexing/Streams per drive

We have found that MPX of 4 gives good backup performance and good restore performance.

My mentor taught me to implement multiplexing in baby steps:
Start with a value of 2.
Record backup performance over the next week (full and incr backups)
Do some restore tests and record performance.

Increase MPX to 3.
Perform same tests.

Increase MPX to 4.
......

Find an MPX value that works best for you.
I have seen customers using MPX of 8 and they were happy with backup and restore performance.

Tape Multiplexing

There is no real fixed rule on this.......... The more you multiplex then longer it takes to restore because the recovery process has to get each data fragment from a tape where they are no longer in a nice sequence suitable for streaming.   I'm running my libraries on a multplex of 24, which is unnaturally high. 

Why :

• Backups are not production and taking far too long.  More streams = quicker backup time.   Restore times for non-production are flexible.
• The tape libraries needs more tape drives to increase throughput.  ATLs are not like disk-based backup targets which have a fixed max throughput capability.
• Data delivery throughput to tape drives could be better.   The more streams you have to better the throughput. 
• About 95% of the servers are small.  Increase the recovery time for a small server by 50% - is anybody going to notice the extra 30 mins? For the large and more critical systems I have reduced multplexing.

Other Stuff

Other things that make ATLs ineffiecient.

• Having too many data retention times. NBU will only write to a tape where the data has the same retention time.  Keep the number rention times to the smallest number possible.  In NBU you can mixed retetion times on a tape but it is not recommmend.
• Set the number of partially full tapes to = (number of tape drives +1 )  this applies to each data retention time.