Writing to tape is slow... looking at tapes in the vendor library UI: most of them are "idle" a majority of the time"

Is there any way to determine where the bottleneck is if CommVault is supposed to be writing data to tapes, but the tape library indicates “the tapes are idle” a lot? My throughput is not great on some of these tape jobs (multiple streams, and multiples... but 50 GB/hr or less on some of them) yet they have TB’s of data to write.  I have heard of a possible “the drives are spinning up and down, wasting time" as a possibility… is there a way to see why CommVault would not be continually writing data, especially if it has multiple streams that are showing “some throughput” in the Java UI, and how one “makes sure commvault is writing data to tape as fast as it can?  I have tried adding more multiplex to the tape job this month and it did not help.