Comment 8 for bug 957494

Then I'm not sure how you got it working ( build mdadm from source? ). Apparently mdadm requires mdmon to do this correctly. Also while mdadm now has the capability to understand Intel arrays, Ubuntu is still built to have dmraid handle them, so there likely will be other problems trying to use mdadm to do so.

Also for what it's worth, unless you need to dual boot with Windows, it is best to avoid the fakeraid setup and just use native mdadm raid. It has much better support and features.