I use RAID 1 and RAID 5 quite a lot on both servers and workstations.
Let's say I want ot have RAID 1 with 100 MB for a small boot partition, 1 GB for swap, and the remaining space for a root partition.
Launch fdisk on the first disk, and create these partitions. As partition type, choose "non-fs-data". Once you've done this, do the same thing on the other disk. Create the exact same partitions.
Now create your arrays:
# mdadm --create /dev/md1 --level=1 --raid-devices=2 --metadata=0.90 /dev/sda1 /dev/sdb1
# mdadm --create /dev/md2 --level=1 --raid-devices=2 --metadata=0.90 /dev/sda2 /dev/sdb2
# mdadm --create /dev/md3 --level=1 --raid-devices=2 --metadata=0.90 /dev/sda3 /dev/sdb3
Make the swap partition manually so the installer will recognize it:
Launch the installer:
Now you can format /dev/md3 using the FS you want (ext4, ext3, whatever). This will be your main partition. Then you can format /dev/md1 as ext2, for example, and use it as /boot partition.
Now you can do the same thing with your personal partitioning scheme.
Beware, though. You *will* need to use the generic kernel with an initrd before the initial reboot, which is a bit tricky.
Another word of caution. When you experiment, you'll probably have to clean up any old array remnants from previous attempts. You'll have to do it like this:
# mdadm -Ss
# mdadm --zero-superblock /dev/sda1
# mdadm --zero-superblock /dev/sda2
# mdadm --zero-superblock /dev/sda3
# mdadm --zero-superblock /dev/sdb1
# mdadm --zero-superblock /dev/sdb2
# mdadm --zero-superblock /dev/sdb3
Last thing: don't forget to deactivate the hardware RAID in the BIOS. Otherwise you'll only see one disk.
: if you don't want to go through all the hassle of a software RAID, just keep the hardware RAID and partition and format your disk as if it was one simple disk. No difference for the installer.