Debian Jessie, raid5 and encryption issues

Question

I installed Debian 8 today. During installation, I made the following settings:

/dev/sda1 -> 1GB /boot
/dev/sda2 -> about 80GB encrypted device
/dev/sda2_crypt -> lvm with VolumeGroup vg0
vg0 -> one logical volume as swap (4GB) and rest as root

System boots up and asks me for my passphrase, as expected. I then added 3x3TB Harddisks in a raid5 array using mdadm and encrypted it using cryptsetup, adding a normal passphrase and also a Keyfile (which was put on the encrypted root partition). I then edited the /etc/crypttab:

raid_data UUID=<uuid> /path/to/keyfile luks

Then rebooted to check if the device gets decrypted and mapped properly.

Unfortunately the only thing that happens is that "a start job is running" in systemd, trying to decrypt the device but for some reason times out after 1m30s. Any help is appreciated.