I have a (remote) Ubuntu 14.04 (XFCE desktop) system which is configured with RAID1 (2 identical disks):
# cat /proc/mdstat Personalities : [linear] [multipath] [raid1] [raid0] [raid6] [raid5] [raid4] [raid10] md0 : active raid1 sda1 sdb1 1953382208 blocks super 1.2 [2/2] [UU]
Inside /dev/md0 is a boot partition (partition 0: 244M), and an LVM VG/PV (partition 5) which contains two volumes: the root system (1.8T) and a swap (12G).
I want to mess with the system (upgrade to 16.04 and then make other changes) and I would prefer to keep the 2nd disk of the raid configuration as a backup so if all goes pear-shaped I can go back to that and recover the original configuration and data.
I read that I can remove the existing RAID configuration with:
mdadm /dev/md1 --fail /dev/sdb1 --remove /dev/sdb1
I'm not sure if I have to do anything to else to stop sdb1 being re-added to the array when the system reboots? For instance
wipefs -a /dev/sdb1 mdadm --grow /dev/md0 --raid-devices=1
I need to be sure that after my work is complete I can either add back /dev/sdb1 to the raid array so that it can be conformed to the (now updated) data in /dev/sda1 or, alternatively, that I can boot from /dev/sdb as the 'old' system and use it to rebuild /dev/sda (if it is in a bad state after a botched upgrade). I realise that booting from /dev/sdb may require local access, but will it be bootable at all when it used to be part of a raid1 device?
Any guidance gratefully received.