Problem with software raid w. Trustix 2.2

Hi,
I?ve created a raid1 software raid with mdadm but can?t bring it to work 
automaticaly after a reboot, always have to give the "mdadm --assemble" 
command to bring it back online. The box is a Dell PowerEdge 1600 the 
system disk is attached to the onboard controller, the raid disks are 
attached to an adaptec 29160. During the boot process I can see that md 
autodect runs before the adaptec driver is loaded. Later during boot 
there is a message "Starting up RAID devices: md0(skipped)".
My /etc/mdadm.conf looks like this:
DEVICE /dev/sda1 /dev/sdb1
ARRAY /dev/md0 level=raid1 devices=/dev/sda1,/dev/sdb1
The mdadm -D -s output when the array is online
ARRAY /dev/md0 level=raid1 num-devices=2 
UUID=8b91a217:3fc89e01:40a627ac:8fe19432
    devices=/dev/sda1,/dev/sdb1
Any ideas what I?m doing wrong?

Regards,

   Mike