I am trying to install Ubuntu 12.04 over Windows 7 using a USB drive. However, I am not able to install it. Installation breaks saying that "bootloader cannot be installed on this device." In the details section, I see the ubiquity message saying that it can't read the partition from dev/sda. I've tried various things, boot-repair one among them (http://paste.ubuntu.com/6056191/), but no luck. What am I exactly doing wrong?
Did you start with clean disks with no partition table on it or did you reuse the disks. This can be the reason why your system won't boot. Guess how I know.
First clean your disks with:
dd if=/dev/zero of=/dev/yourdev bs=512 count=1
replace yourdev with the device name of your disks
Then install Ubuntu again. It will then install new gpt partition tables. You only need a swap and a boot partition in raid ofcourse.
Don't forget to adjust your uefi settings in the bios.