Description:
------------
Running disk_total_space on a system that is using LVM it will return completely 
incorrect data.
For example on a machine with result of "df -h" as follows:
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/vg-vg_root    99G   47G   47G  50% /
tmpfs                     32G     0   32G   0% /dev/shm
/dev/sda1                194M   65M  120M  36% /boot
/dev/mapper/vg-vg_backup 400G   33M  400G   1% /var/tmp
/dev/mapper/vg-vg_mysql  950G   81G  870G   9% /data

on this setup it will always return 32G.

We get similar result on second machine with "df -h":
Filesystem              Size  Used Avail Use% Mounted on
/dev/mapper/batty-root  258G  217G   29G  89% /
none                    4.0G  208K  4.0G   1% /dev
none                    4.0G     0  4.0G   0% /dev/shm
none                    4.0G   88K  4.0G   1% /var/run
none                    4.0G     0  4.0G   0% /var/lock
none                    4.0G     0  4.0G   0% /lib/init/rw
none                    258G  217G   29G  89% /var/lib/ureadahead/debugfs 

where it will always return 4G.

At first that it was because of outdated version of PHP, original tests were 
with PHP version 5.3.27 and 5.3.6, but then I was able to reproduce it on my 
testing box with Gentoo and PHP 5.4.17.