#!/usr/bin/sh

rpm --root /mnt -qa --queryformat "%{SIZE}\n" | perl -ne '$i += $_; END { print int $i / 1024, "\n" }'
df | grep "/mnt$" | perl -ane 'print "$F[2]\n"'

#ext2
#   95360  145900
#  222216  293364
#  446309  564616
#  759873  971240
#  815171  990816
#  978942 1161900
# 1134733 1358620
# 2071922 2405024

#reiserfs (notail)
#  95661 146296 468016
# 224262 293076 321236