Re: Can I use software RAID mdadm this way?
Assuming that I used mdadm during my install of Ubuntu 12.04, then yes. I have 2 HDD each with 2 500GB partitions. From that, I was able to raid one partition from each physical drive and create two raids on half of each HDD. It works fine so there should be no reason why you can't raid just your 500GB HDDs without affecting your current installation. I don't know how to raid with mdadm, it will be easier if you just did a reinstall and setup the raid then (unless you find a really good guide online). You will need the alternative version of Ubuntu to be able to setup raid during the installation.
♫♪♫ You just keep on trying till you run out of cake ♪♫♪