amazon ec2 - Disk size and space detection

i'm running a server with debian stable
:

Linux myhostname
2.6.32-5-xen-amd64 #1 SMP Tue Mar 8 00:01:30 UTC 2011 x86_64
GNU/Linux

It is running a nginx,
mail server,ftp server and a mysql
database.

This morning postfix complained it''s
running out of space, so I double checked the free storage and it is as
such

root@myhostname:# cat
            /etc/fstab 
/dev/xvda1 / ext3 defaults 1 1
/dev/xvda2 /mnt ext3
            defaults 0 0

/dev/xvda3 swap swap defaults 0 0
none /proc
            proc defaults 0 0
none /sys sysfs defaults 0
            0


root@myhostname:# cat /etc/mtab
/dev/xvda1 /
            ext3 rw 0 0
tmpfs /lib/init/rw tmpfs rw,nosuid,mode=0755 0 0
proc
            /proc proc rw,noexec,nosuid,nodev 0 0
sysfs /sys sysfs rw,noexec,nosuid,nodev
            0 0

udev /dev tmpfs rw,mode=0755 0 0
tmpfs /dev/shm tmpfs
            rw,nosuid,nodev 0 0
devpts /dev/pts devpts rw,noexec,nosuid,gid=5,mode=620 0
            0
/dev/xvdf /mnt ext4 rw 0
            0

So "/dev/xvdf" is a
big hdd (500GB) mounted on /mnt and it is where all the stuff related to the webservice
is stored, "/dev/xvda1" instead is mounted in the root filesystem and it is an amazon
aws standard image ami, 8GB, both of them should have enough free space
but:

root@myhostname:# df
            -h
Filesystem Size Used Avail Use% Mounted on

/dev/xvda1
            1008M 1008M 0 100% /
tmpfs 306M 0 306M 0% /lib/init/rw
udev 286M 32K
            286M 1% /dev
tmpfs 306M 0 306M 0% /dev/shm
/dev/xvdf 493G 1.1G 467G
            1% /mnt

root@myhostname:# fdisk -l /dev/xvda1
Disk
            /dev/xvda1: 8589 MB, 8589934592
            bytes

I'm
pretty sure that /dev/xvda is 8GB capacity but for some reason the system sees only 1GB
and it is now entirely filled, any ideas why?