geli encrypted memory disk?

[Frank J. Beckmann]

Hi,

after upgrading to FreeBSD 6.0-BETA4 from the 17th I wanted to play a bit with 
geli. First try was an encryptet memory disk.

dd if=/dev/zero of=/var/sdisk bs=2028 count=220
mdconfig -a -t vnode -S 2048 -f /var/sdisk -u 3
geli init -a AES -s 2048 /dev/md3

Geli asks me the new password twice and then exits with the following error:

Cannot store metadata on /dev/md3: Invalid argument.

What am I doing wrong?
-- 
Greetings
Frank