Solved it....
I have to format my raid array ofcourse:
mke2fs /dev/md0
============================================
more /proc/mdstat:
Personalities : [raid5]
read_ahead 1024 sectors
md0 : active raid5 hdd5[2] hdc5[1] hda5[0]
240107136 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
[===>.................] resync = 18.2% (21885536/120053568) finish=174.9min speed=9350K/sec
unused devices:
============================================
df:
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/sda3 17291004 5407576 11005076 33% /
/dev/sda1 101089 8838 87032 10% /boot
none 257208 0 257208 0% /dev/shm
/dev/md0 236339584 20 224334208 1% /mnt/md0
============================================
more /etc/raidtab
#
# EvG: This is the configuration file for the RAID 5
#
raiddev /dev/md0
raid-level 5
nr-raid-disks 3
nr-spare-disks 0
persistent-superblock 1
parity-algorithm left-symmetric
chunk-size 64
device /dev/hda5
raid-disk 0
device /dev/hdc5
raid-disk 1
device /dev/hdd5
raid-disk 2