Much has been written on this subject already yet it continues to be a topic fraught with pitfalls and mired in confusion. Perhaps by describing the way NetBackup's tape writing (as implemented in bptm process) operates some of this veil can be lifted and tape drives can be made to hum more efficiently.

For each NetBackup job stream writing to tape, a bptm process is launched. Part of its launch information packet includes a description of the source of its data, i.e. the client machine, the NetBackup policy and schedule, etc. However, the first bptm process does not directly concern itself with contacting the client, instead, it forks off a child process to start listening on a predetermined TCP/IP socket for the client to contact it. The parent process meanwhile proceeds to allocate, open and otherwise prepare a tape and a tape drive to start writing the eagerly anticipated client data.
Next comes the description of how to the two pass this client data between eachother.

Anyone with more than one backup tape volume will have a need to apply labels to keep them straight. If nothing else because that is how all backup software refers to the tapes it writes and, hopefully, reads.

Run enough tapes through tape drives and eventually the accumulated dust and rubbed of tape particles will affect the drives' ability to read and write. The good news is that all modern tape drives have a read-behind-write design which allows them to detect this condition. When a head-cleaning is required these drives will send out an alert on their SCSI bus.
The response to this SCSI alert depends on how NetBackup and the hosting robot, where applicable, are configured. Read on to see what your options are: