First of all I want to thank to this howto and also to the comments as I'm quite new to linux, and found them VERY usefull.

Now to add my 2 cents, I will just tell my little experience with RAID

I had to build a server and the hardware turn to be a FakeRAID one, so at a first attempt I thought to give it a try to FakeRAID, issued a dmraid -ay from the LIVE CD and play a little with it. Then after some reading about pro/cons of FakeRAID vs Software RAID, I made my mind and took the software RAID path, as I wanted to have RAID10 as root filesystem Ive made 2 partitions more or less like in one of this comments is recommend, I formatted then, run the server installer, partitionated in manual, and all installs ok.

Then I boot and...

Initramfs appears (what the heck is this? was my first thought)

well there Ive tried mdadm --assemble --scan , answers "no device found"

To making it short, after 2 days of swering and with quite some less hair in my head I found the culprict

dmraid

The ubuntu boot takes up dmraid and it gets the devices for him even if I actually not used it for the install, I had to chroot, then dmraid -an , apt-get remove dmraid, and my problem solved, as I didn't found this anywhere, I thought it can help others 

Hope it helps someone

Fer