>Can you tell me exactly why it is wrong to clean every X hours of
>operation? I sorta need to justify this to my boss who sees the only
>harm in doing it every X hours as using up a lot of cleaning
>tapes.

The cleaning tape is abrasive and as such it will contribute to the 
wearing out of the expensive little heads of your expensive little 
DLT drives. :)

>Whereas on the other hand, if you have the have the hardware
>clean the drives, you have no way of knowing when to change the tape,
>right? Or does NetBackup still know the number of cleanings, etc.

Something that Curtis didn't mention (I bet he wasn't aware of the 
functionality, as it's certainly never made clear in the NetBackup 
GUI, but it's mentioned on p.309 of the Media Manager 3.2 Admin 
Guide) is the fact that NetBackup can control the cleaning tape *no 
matter which method you choose* - time-based or demand-based.

This is the way to have your cake and eat it too:

    -turn off autoclean on your tape library
    -insert a cleaning tape into your library and configure a
     Netbackup volume of type "DLT-CLN"
    -for each of your DLT drives in this library, set the
     "Cleaning Frequency" to 0
    -set up some sort of cronjob (you can use the 
/usr/openv/netbackup/bin/cleanstats, or write your own based on it) 
that will periodically check the cleaning tape and raise an alarm 
when it's about to run out.

voila.  when one of your DLT's needs cleaning, a TapeAlert signal 
will get sent, NetBackup will clean the drive, and after this happens 
frequently enough, your cron job will email you that your cleaning 
tape needs to be replaced.  (note that this implies that you're 
running NBU 3.2 - I'm not sure if NBU <3.2 supports TapeAlert or not)

HTH
rob