[CentOS] Command to get tape capacity status?

I have an Overland tape library connected, via SCSI card, to an 
out-of-box, full install of C5 install on an old PC.

I have a script that uses tar to archive data to tape and mtx to change 
tapes.  What I don't know, if possible, is to obtain the status of how 
much tape is left in the drive.   If I get a write failure, I'd like to 
know if the tape is bad or has run out of space.

I know of bacula, amanda, and other backup methods, but I prefer to use 
the simplest options possible, mainly because if a hard drive failure 
occurs, which has happened at the last minute, I can take the original 
C5 media from CD, install it, and get back up and running in no time.

So, any way to inquire remaining tape status and [estimated] capacity?

Thanks.

Scott