> I have no understanding of this. I've never seen a df output
quoted text
> that tells me I'm using 13GB more space than the drive is
> capable of holding.
> 
> I ask here because there's obviously potential for me to lose
> data somewhere down the line. I'll be grateful if anyone can
> explain where I've gone wrong.
> 

You can zero the disk device directly but use bs=2m to speed it up or
use the file you've created as an encryption device with vnconfig.

There are a few ways of encrypting though.

Don't worry the -13G is perfectly normal.

275 * 0.05 = 13.75 ie 5% is reserved as root for stability and
important work, had you written the file as a normal user you would have
had 0 space left and be using 261Gs of 275.

Lookup up the faq or previous mails at marc.info as I'm sure the answer
is in both.