Disk volume calculation

Hello everybody,

I would like to know how Solarwinds calculates the disk volume ?

It seems it is : (disk used / total disk) * 100.

But when I look server's value, it isn't the same.

Here are the stats in Solarwinds :

Here are the stats from the server :

root@blablabla   df -h

Filesystem            Size  Used Avail Use% Mounted on

/dev/mapper/VolGroup00-lv_root

                      159G  138G   13G  92% /

So there are 5% missing in Solarwinds side.

Any idea?

Regards