I was surprised to see that Linux Mint at the latest 17.2 version still has NO mdadm installer option, and worse the installer will not be able to create a proper booting environment even when you do install it.
How to setup mdadm in Linux mint LiveCD
apt-get install mdadm
# partition as you need and then create your mdadm devices
# create your SWAP md0
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1
# create your boot md1 (remember to use the --metadata=0.90 or it will not be bootable and it must be RAID 1 as RAID 10 cannot be booted
mdadm --create /dev/md1 --level=1 --metadata=0.90 --raid-devices=2 /dev/sda2 /dev/sdb2
# create root mdadm md2
mdadm -create /dev/md2 --level=10 --layout=f2 --raid-devices=2 /dev/sdb3 /dev/sdb3
Run the installer
Double click each mdadm array to create the appropriate partition (eg. md0 is swap, md1 is /boot and md2 is /)
Choose to install the boot loader on sda (it doesn't really matter because it will not succeed or work even if Linux Mint says it did).
The Most Crucial Part, to chroot and install the necessary utilities
I admit I spent a few days sorting this out because I have never had a problem in the past normally installing grub 0.97 by using the old manual way. Linux mint uses the newer grub2 and is more complex/picky but also does it all for you as long as you do it as below.
mount /dev/md2p1 /mnt
# do not forget to mount your /boot or grub-install will NEVER work
mount /dev/md1p1 /mnt/boot
for bind in dev sys proc; do
mount -o bind /$bind /$mount/$bind
apt-get -y install mdadm grub2
#change the grub-install portion to match the physical devices that make up your boot partition and make sure you just point to the raw disk and not a specific partition
#the above last command should do it and get you booting
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