Building an additional raid

My box already had two hard disks in raid10. Wanted to add two more disks in a second raid. Here is what I did. This was on Ubuntu Trusty.

• Boot with Ubuntu install CD
• Go into recover mode
• Navigate until you hit the partition disk option (had to go forward and backward in the wizard to end up here!)
• Perform the partition as you would on a new system, except only do it for the two new disks and leave the existing untouched
• When asked to specify mount point specify / (root)
  • Specifying root is not what I actually wanted as this was a supplementary data disk (set)
  • The install (even recover mode) would not let me proceed if I did not have a root partition mount
• Confirm the write to partition table
• The system will start installing the OS on the new root partition! Not what we wanted of course.
• Press reset (Ctl-Alt-Del) in the middle of the install to force reboot!
• Boot back into the system (as before) with your regular boot disk
• Run fdisk -l to check that disks are raid are all in place - should be or something went awry
• Use blkid to determine the UUID of the new raid disk set
• Update /etc/fstab with mount point (create the mount-point directory first)
• Issue a mount -a to mount the disks
• Remove the frivolous install files that the Ubuntu installer started to copy in the new set of disks
• Issue a cat /proc/mdstat to observe raid sync process
• Issue a mdadm –detail –scan to get the new (and existing ARRAY) details
• Update /etc/mdadm/mdadm.conf with the new ARRAY details
• Run update-initramfs -u to add it to the initramfs image

I used the install CD as the process is standard and you can do it via a tool as opposed to commands, that I could not find a good comprehensive set of. It is sort of imperfect in that you have to fool the installer into just creating your raid/partitions and force abort the actual install. However it works and does not have any risk.