RAID 1

[Tom H]

On Thu, Oct 7, 2010 at 6:19 AM, GeraldCC <gcsgcatling at bigpond.com> wrote:
>
> Is raid 1 safe to use in Ubuntu/Kubuntu?
> I am reading the Ubuntu Server Administration (8.04 LTS)
> Raid 1 appears to be recommended in this tome, but trying it in PCLinuxos
> 2010.07 has given a lot of heart ache. If one removes the second drive in the
> array, then powers up again the system still runs BUT shutting down again and
> re-inserting drive 2 and trying to add it to the raid array I need to reformat
> the first drive to add the second and also format the second drive...So loosibg
> everything.
> This does not seem to be the case in Ubuntu?
> But is it OK and safe to use raid 1?

I've never used PCLinuxOS but I doubt that you lost everything because of it.

Assume that you have your system's root on /dev/md1 constituted of
/dev/sda1 and /dev/sdb1.

If you shutdown the box, pull out /dev/sda, and reboot, the box will
come up (assuming that grub is set up properly) using /dev/sdb1. If
you then shutdown, re-insert /dev/sda, and reboot, the box will come
up using /dev/sdb1 with /dev/sda1 available (and possibly even
assembled into its own, new, one-disk RAID 1 md device, /dev/mdX). If
/dev/sda1 is a member of /dev/mdX, you have to run "mdadm --stop
/dev/mdX", otherwise you can skip this step. You then run "mdadm
/dev/md1 --add /dev/sda1" to add /dev/sda1 to /dev/md1. You have to
ensure that the mirror syncs before pulling any disk out again.

The proper way to remove a disk from an array is, even if disk dies,
to run "mdadm /dev/md1 --fail /dev/sda1; mdadm /dev/md1 --remove
/dev/sda1".