> 
> Hello all,
> 
> This is not likely a bacula questions, but in the chance that it is, or the
> experience on this list, I figured I would ask.
> 
> We've been using LTO3 tapes with bacula for a few years now.  Recently I've
> noticed how variable our tape capacity it, ranging from 200-800 Gb.
>   Is that strictly governed by the compressibility of the actual data being
> backed up?  Or is there some chance that bacula isn't squeezing as much
> onto my tapes as I would expect?
> 
> 200Gb is not very much!
> 

I don't think this explains your issue, but LTO drives will write the data to 
the tape, and then immediately read it again (the read head is placed such that 
this is possible). If the read is bad the drive will rewrite the data. This 
ensures that you get a good write, but obviously decreases the effective 
capacity of your tape.

Your tapes would have to be pretty worn out to drop the capacity to 25% though.

The tape and/or drive should record the margin and other figures, but I don't 
know of any Linux tools to read that information.

James


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