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?