Pre-

1. Make a bootable usb key with Ubuntu 14.04.5 desktop installed.
2. Two hard disks:

/dev/sda 100GB
/dev/sdb  50GB

Configuration

/home 50GB RAID1
/     40GB 
/boot  1GB
swap   9GB

Installing

step 1: boot to your usb driver. (use BISO)

step 2: try ubuntu

step 3: open a terminal. Clean your drivers.

sudo sgdisk -Z /dev/sda
sudo sgdisk -Z /dev/sdb

step 4: connect to internet.

step 5: install the RAID manager with default configuration

sudo apt-get install mdadm

step 6: partition the drivers: /dev/sda and /dev/sdb

$ sudo fdisk /dev/sda
  n
  p
  1 # <- sda1
  2048
  +50G  # <- sda1 with 50GB for /home on RAID1
  n
  p
  2 # <- sda2
  [enter] # <- press enter on your keyboard
  +1G # <- sda2 with 1GB for /boot
  n
  p
  3 # <- sda3
  [enter] # <- press enter on your keyboard
  +40G # <- sda3 with 40GB for /
  n
  p
  4 # <- sda4
  [enter] # <- press enter on your keyboard
  [enter] # <- press enter on your keyboard,for Swap 
  w

$ sudo fdisk /dev/sdb
  n
  p
  1 # <- sdb1
  2048
  +50G # <- sdb1 with 50GB for /home on RAID1

step 7: create RAID 1

sudo mdadm --create /dev/md0 --l 1 -n 2 /dev/sda1 /dev/sdb1

* step 8*: create partitions on /dev/md0

$ sudo fdisk /dev/md0
  n
  p
  1
  [enter]
  [enter] # <- md0p1 is ready 

step 9: start to install ubuntu on your hard drivers.
use manual partitioning. configure each driver:
Just select corresponding driver,choose use as ext4 or swap,check the format Box.

step 10 : once you finish the installation,do not reboot. The following steps is very important!

sudo -s
mount /dev/sda3 /mnt
mount -o bind /dev /mnt/dev
mount -o bind /dev/pts /mnt/dev/pts
mount -o bind /sys /mnt/sys
mount -o bind /proc /mnt/proc
cat /etc/resolv.conf >> /mnt/etc/resolv.conf
chroot /mnt
apt-get install mdadm vim
vim /etc/grub.d/10_linux # change quick_boot to 0
grub-install /dev/sda
grub-install /dev/sdb
update-grub
sudo shutdown -r now

Enjoy it !