`./md0 /mnt /dev/xvdb /dev/xvdc /dev/xvdd`

md0.sh

#!/bin/bash

mount=$1; shift
devices=$*

if [[ -z $devices ]]; then
  echo $0 /dev/DEV [/dev/DEV]
  exit 99
fi

sw="$#"

echo $sw $devices

sudo apt-get -q update >/dev/null
sudo apt-get install -q --no-install-recommends mdadm xfsprogs

firstdev=`echo $devices | cut -d' ' -f1`

if ! mount | fgrep " $mount " && [ -b $firstdev ]; then
  echo making $mount
  [ -d $mount ] || sudo mkdir $mount

  echo creating array
  /usr/bin/yes | sudo /sbin/mdadm --create /dev/md0 --level=0 -c256 --raid-devices=$sw $devices

  echo making mdadm.conf
  echo "DEVICE $devices" | sudo tee /etc/mdadm/mdadm.conf
  echo "MAILADDR root" | sudo tee -a /etc/mdadm/mdadm.conf
  sudo sh -c "/sbin/mdadm --detail --scan >>/etc/mdadm/mdadm.conf"

  echo update-initramfs
  sudo update-initramfs -u

  sudo blockdev --setra 512 /dev/md0
  sudo mkfs -t xfs -f -d su=256k -d sw=$sw /dev/md0

  sudo mount -t xfs -o noatime /dev/md0 $mount
  fgrep /md0 /etc/fstab || sudo sh -c "echo /dev/md0  $mount  xfs    defaults,noatime,nobootwait 0 0 >>/etc/fstab"
fi