How to mount an existing RAID device after a clean installation of Ubuntu?

view story

http://askubuntu.com – So I created a RAID device (RAID5 with 4 drives) on Ubuntu 10.04. I did an upgrade to 12.04 but failed and the system won't boot correctly anymore. I am thinking about to do a clean installation of Ubuntu 12.04, but how do I use the existing RAID device and make sure the data on it are intact? (HowTos)