Seems there was a problem with the drive I was using. I tried it with another drive and everything works.
Thank you all for the good help!
Thank you! I was able to connect to it by using cmd+k and connect to afp://192.168.0.205 (ip from the raspberry)
(stupid of me not to try that)
Now i'm connected but i don't have privileges to write something to the drive.
I've created a user and gave it privileges to write on the disk (see screenshot).
I installed OMV on my raspberry pi (omv 1.12). I've also installed the netatalk plugin and enabled it. (see attachments)
I can see the afp share on my mac but i can't connect it. I'm running OSX 10.10.2.
Is this a known issue or is there a problem with my configuration?