eh hehe

mount-ephemeral-xfs.sh

#!/bin/bash -ex

METADATA_URL_BASE="http://169.254.169.254/2012-01-12"

if [[ $# -eq 0 ]]; then
  echo "Usage: mount-ephemeral.sh ROOT"
  exit 1
fi

ROOT=$1

existing_count=$(find $ROOT -maxdepth 1 -type d | wc -l)
existing_count=$((existing_count - 1))

if [ $existing_count -gt 0 ]; then
  echo "Ephemeral drives already mounted, exiting."
  exit 0
fi

root_drive=`df -h | grep "/dev/xvda1" | awk 'NR==1{print $1}'`

if [ "$root_drive" == "/dev/xvda1" ]; then
  echo "Detected 'xvd' drive naming scheme (root: $root_drive)"
  DRIVE_SCHEME='xvd'
else
  echo "Detected 'sd' drive naming scheme (root: $root_drive)"
  DRIVE_SCHEME='sd'
fi

# figure out how many ephemerals we have by querying the metadata API, and then:
#  - convert the drive name returned from the API to the hosts DRIVE_SCHEME, if necessary
#  - verify a matching device is available in /dev/
drives=""
ephemeral_count=0
ephemerals=$(curl --silent $METADATA_URL_BASE/meta-data/block-device-mapping/ | grep ephemeral)
for e in $ephemerals; do
  echo "Probing $e .."
  device_name=$(curl --silent $METADATA_URL_BASE/meta-data/block-device-mapping/$e)
  # might have to convert 'sdb' -> 'xvdb'
  device_name=$(echo $device_name | sed "s/sd/$DRIVE_SCHEME/")
  device_path="/dev/$device_name"

  # test that the device actually exists since you can request more ephemeral drives than are available
  # for an instance type and the meta-data API will happily tell you it exists when it really does not.
  if [ -b $device_path ]; then
    echo "Detected ephemeral disk: $device_path"
    drives="$drives $device_path"
    ephemeral_count=$((ephemeral_count + 1 ))
  else
    echo "Ephemeral disk $e, $device_path is not present. skipping"
  fi
done

if [ "$ephemeral_count" = 0 ]; then
  echo "FAILURE: No ephemeral disks detected!"
  exit 1
fi

# Unmount default ephemeral0 mount if it exists
umount /mnt || true

# Create filesystems on drives and mount
drive_count=0
for drive in $drives; do
  mkdir -p $ROOT/$drive_count
  mkfs.xfs -f $drive
  mount_point=$ROOT/$drive_count
  mount -t xfs -o noatime $drive $mount_point
  drive_count=$((drive_count + 1))
  echo "Mounted $drive to $mount_point"
done