GPT partitioning function

write_gpt.sh

#!/bin/bash

# Compute partition sizes based on system memory (swap) and disk size.
# There is no /boot because grub2 uses the BIOS Boot Partition (EF02)
# to write out the payloads that used to have to be in /boot at the
# front of the disks.
# The EFI Partition will end up unused on all of our legacy BIOS-only
# systems, but it's only 128MB and can remain consistent as the EFI/UEFI
# systems take over.

write_gpt () {
  device=$1
  name=$(basename $device)
  # get the size of the disk in bytes
  disk_bytes=$(blockdev --getsize64 $device)
  # the last sector isn't always (or ever) size/sectorsize
  last_sector=$(blockdev --getsize $device)
  # this should support 4k sectors automagically
  ss=$(blockdev --getss $device)
  # measure RAM to use for swap size
  ramkb=$(awk '/MemTotal:/{print $2}' < /proc/meminfo)
  rambytes=$((ramkb * 1024))

  # BIOS Boot (for grub2), 1MB
  bios_start=2048
  bios_end=$((bios_start + 1048576/ss))

  # EFI partition, 128MB
  efi_start=$((bios_end + 1))
  efi_end=$((efi_start + 134217728/ss))

  # Linux root RAID1, 40GB or 1/2 remaining disk, whichever is smaller
  remaining=$((last_sector - swap_end))
  half_remaining=$(((remaining-remaining%2)/2))
  root_start=$((efi_end + 1))
  root_end=$((root_start + 42949672960/ss))

  # when testing, I may have way less than 40GB for speed, so
  # split remaining space in half between root/data if that happens
  if [ $((root_end - root_start)) -gt $half_remaining ] ; then
    root_end=$((root_start + half_remaining))
  fi

  # Linux swap, 1x RAM or 10% of HDD, whichever is smaller
  swap_start=$((root_end + 1))
  swap_sectors=$(((rambytes-rambytes%ss)/ss))
  max_swap_sectors=$(((last_sector-last_sector%10)/10))
  if [ $swap_sectors -gt $max_swap_sectors ] ; then
    swap_end=$((swap_start + max_swap_sectors)) # 1/10th disk, probably only in test VM's
  else
    swap_end=$((swam_start + swap_sectors)) # 1x RAM
  fi

  # RAID1 Data Partition
  data_start=$((swap_end + 1))
  data_end=0

  # clear & create a new GPT label
  sgdisk -Z $device
  sgdisk -og $device

  # create partitions
  sgdisk -n 1:$bios_start:$bios_end -c 1:"BIOS Boot Partition"  -t 1:ef02 $device
  sgdisk -n 2:$efi_start:$efi_end   -c 2:"EFI System Partition" -t 2:ef00 $device
  sgdisk -n 3:$root_start:$root_end -c 3:"Linux Root RAID1"     -t 3:fd00 $device
  sgdisk -n 4:$swap_start:$swap_end -c 4:"Linux Swap"           -t 4:8200 $device
  sgdisk -n 5:$data_start:$data_end -c 5:"DATA RAID1"           -t 5:fd00 $device
  sgdisk -p $device
}