With new grml 2010.04 mdadm creates a metadata layout which is incompatible with 
default debian lenny.

Raid 1 created with default settings can not be booted anymore with either grub 
or grub2 from lenny. It gives strange error messages on grub-install with 
something like "no mapping for device (md0) found".
This is not correctable without recreating the whole array.

mdadm --create needs an additional parameter -e0 to create metadata version 0.90.