It is important to be able to cope with the failure of a faulty disk.

As the enclosure being used may not support hot-swapping and there may not be a separate light for each disk, there needs to be a way to determine which disk has failed and needs to be replaced.

mdadm --detail /dev/md0

Steps are:

• Wait until the disks has finished rebuilding on the spare disk if any.
• Power the server down.
• Replace the faulty disk.
• Power the server up again.
• Partition the disks.
• Add the new disk to the array with:

  mdadm --add /dev/md0 /dev/sdd1