df(1) and missing space in partition /dev/ada0p2

[Robert Bonomi]

> From owner-freebsd-questions at freebsd.org  Sun Jul  8 01:46:23 2012
> Date: Sun, 8 Jul 2012 08:44:51 +0200
> From: Matthias Apitz <guru at unixarea.de>
> To: freebsd-questions at freebsd.org
> Subject: df(1) and missing space in partition /dev/ada0p2
>
>
> Hello,
>
> I hace setup a fresh 10.0-CURRENT, this time using gpart(8) and I do not 
> understand why the sum of Used and Avail does not equal to the full space 
> of /dev/ada0p2:
>

A traditional UFS filesstem reserves the last 10% of the disk capacity for 
the exclusive use of the superuser.  'Avail' represents the space that is
available to _any_ user.  Thus, on an absolutely _empty_ filesystem,
'avail' will be only 90% of 'total'.

'man tunefs' and see 'minfree' for  the gory details.