Adding Additional RAID Array for Storage in Ubuntu 11.10 x64 Server

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http://askubuntu.com – Haven't run into this situation before but it seems simple enough. Looking for advice/guidance on the following issue. I have an Ubuntu 11.10 64-bit server that is configured with 2 identical hard drives in a RAID-1 through the mdadm utility. It's a simple LAMP server that runs a few projects I'm working on but is growing out of the current storage. What I would like to do is install 3 additional hard drives as a second array using mdadm and RAID-5 and have it accessible as /sites (or something similar). I would then like to then move the contents of the projects on the RAID-1 to this new big (HowTos)