Assuming you have an EBS instance for the root filesystem, and you want to mount your SSDs (on /dev/xvdb and /dev/xvdc) as raid0 every boot/reboot.
Remove the last line of /etc/fstab that refers to /dev/xvdb, and unmount your devices if they are mounted.
umount /dev/xvdb
umount /dev/xvdc
mdadm isn't installed by default.
apt-get install mdadm -y
We're going to mount at /u01
mkdir /u01
Create an upstart configuration to re-initialise the raid device on every boot.
cat > /etc/init/mount-ephermal-ssd.conf <<HERE
start on virtual-filesystems
script
# Attempt a short circuit mount - one of these works
# after a reboot
mount /dev/md127 /u01 && exit
mount /dev/md0 /u01 && exit
# It's possible this was a EC2 STOP/START - create everything from scratch
# Although we specify md0, the actual device may be md127 upon reboot!!!
yes | mdadm --create --verbose --force /dev/md0 --level=0 --raid-devices=2 /dev/xvdb /dev/xvdc
# Last chance
mount /dev/md127 /u01 && exit
mount /dev/md0 /u01 && exit
# Clean FS
mkfs.ext4 /dev/md0
mount /dev/md127 /u01 && exit
mount /dev/md0 /u01 && exit
end script
HERE
Now just reboot (to test it all works)