Linux root disk resize with raid, ext4 and grub2

There are lots of decent how-to pages on the 'net;

• http://www.howtoforge.com/how-to-resize-raid-partitions-shrink-and-grow-software-raid
• http://michael-prokop.at/blog/2006/09/09/raid5-online-resizing-with-linux/
• https://raid.wiki.kernel.org/index.php/Growing  <----- This is the best one.

And here are my notes;

• Make sure you add a small <5MB partition for the boot loader as these are the boot disks
  
  # gdisk -l /dev/sdc
  GPT fdisk (gdisk) version 0.5.1
  
  Partition table scan:
    MBR: protective
    BSD: not present
    APM: not present
    GPT: present
  
  Found valid GPT with protective MBR; using GPT.
  Disk /dev/sdc: 1953525168 sectors, 931.5 GiB
  Disk identifier (GUID): 1213CECB-D072-12C2-4846-60804FA91405
  Partition table holds up to 128 entries
  First usable sector is 34, last usable sector is 1953525134
  Total free space is 0 sectors (0 bytes)
  
  Number  Start (sector)    End (sector)  Size       Code  Name
     1              34            6144   3.0 MiB     EF02  BIOS boot partition
     2            6145      1953525134   931.5 GiB   FD00  Linux RAID
  
  
• Set the grub_bios flag on the small partition
  
  sudo parted /dev/sdc set <partition_number> bios_grub on
  
• Once you have swapped out the disks each time, re-sync-ed and grown the raid.
  Boot via a rescue disk and fsck the raid metadevice and then resize the filesystem.
  
  e2fsck -f /dev/md0
  
  resize2fs /dev/md0
  
  mkdir /tmp/a
  mount /tmp/a /dev/md0
  df -h
  
•  Reboot and you are done.
  
  # df -h | egrep "md|Filesys"
  Filesystem            Size  Used Avail Use% Mounted on
  /dev/md0              917G  8.0G  863G   1% /
  /dev/md2              1.8T  456G  1.3T  27% /data

Resync on the old disks

md0 : active raid1 sdd1[2] sdc1[0]
      74920896 blocks [2/1] [U_]
      [>....................]  recovery =  2.6% (2012992/74920896) finish=41.5min speed=29240K/sec

Resync on the new

md0 : active raid1 sdd2[1] sdc2[0]
      976759424 blocks [2/2] [UU]
      [=>...................]  resync =  8.1% (79639488/976759424) finish=181.6min speed=82296K/sec

Some what faster - and a hell of a lot quieter.