Comment 29 for bug 666577

As phillip previously said there is a dm-raid456 on the way (dm-raid is the module and it exists in 2.6.38 but is still listed experimental).

I believe that most standard RAID5 arrays do work or we would see more bugs (RAID5 is a common setup with dm).
Obviously yours is a special case and requires some work to get the dmraid driver working correctly.

What are the errors with 11.04?

Ubuntu at the end of a the day is a 'bleeding edge' distrobution, many of the new features included in it have not been tested longer than a few months and although most bugs are fixed before release some of the lesser used features can end up with regressions. You can always choose a more stable distro like debian if you are looking for ultimate stability.