Steps for replacing hard drives in an mdadm RAID1:


1. mdadm-fail the bad drive:

	mdadm --manage /dev/mdX --fail /dev/sdXY

2. mdadm-remove the bad drive:

	mdadm --manage /dev/mdX --remove /dev/sdXY

3. Make sure whichever drive is active can be booted,
   power off the machine, replace the failed drive,
   power on the machine

4. Create partitions on the new drive

5. Add the new drive's partitions to the appropriate RAID arrays

	mdadm --manage /dev/mdX --add /dev/sdXY

6. Wait for resync

7. Repeat steps 1-6 for the good drive's replacement

8. mdadm-grow the newly synced array:

	mdadm --grow /dev/mdX --size=max

9. Wait for resync

10. Grow the filesystem on the new array