How to determine how much of a tape is used up?

[Halogenic]

BE 11d.  I've got a full backup that takes 2 tapes.  I put in one at  night and in the morning swap in the next one.  The backup finishes in fairly short order and I'm thinking that there isn't much data on the 2nd tape.  

Out of curiosity, how can I tell how much data is put onto that 2nd tape?

Reason I'm asking is I want to know when that 2nd tape gets close to being full so that I can trim out stuff being backed up.  Because it'll be a hassle if I have to go to a 3rd tape for the backup to complete.

[roeme]

That's easy.
In BE, goto "Media". There, select the Media Set where the meda is assigned to. On the upper left, you'll see a list of all the media, and a column that says "Used Capacity." You may need to scroll to the right, tough. If you don't see this column, you can make it visible the standard "Microsoft Windows"-way.

[Ken_Putnam]

If you are using software compression roeme's solution will work 

if you are using hardware compression, there is no way for BackupExec to know how much compression is being acheived, so no way to calculate the "free space"  on the tape volume