Configuring RAID1 after install

[Patrick Siglin]

Yeah that sounds like it would work. Just doing it backwards. I never
thought about that. Good call.

-----Original Message-----
From: ubuntu-users-bounces at lists.ubuntu.com
[mailto:ubuntu-users-bounces at lists.ubuntu.com] On Behalf Of Ewan Mac Mahon
Sent: Saturday, March 18, 2006 4:00 PM
To: ubuntu-users at lists.ubuntu.com
Subject: Re: Configuring RAID1 after install

On Sat, Mar 18, 2006 at 02:44:08PM -0600, Patrick Siglin wrote:
> On Saturday, March 18, 2006 2:14 PM John Lyon wrote:
> > On 3/18/06 1:41 PM, "Patrick Siglin" <poison at list.memphistw.org>
> > either wrote, forwarded or quoted:
> 
> > > Are you talking software raid? I am doing a hardware raid with an
> > > adaptec ata raid controller. I installed mine after the fact and
> > > told my controller to mirror.
> 
> > Yes, software raid. 

> Yeah I don't think you can do it. If there is a trick I would like to
> know also.

OK; presumably you've got one disk at the moment, and you're planning to
add a second to create the mirror? If this is the case then you install
the second disk, partition it (optionally) and then create the RAID on
it, but telling mdadm to create the array in degraded mode (ie create a
two disk array, but with one disk missing, so only actually using one
disk).

At this point you've got a working RAID 'array', albeit only actually on
one disk, and your old system on its original disk. Copy the complete
contents of the system from the old place to the new (carefully), then
reboot, booting from the array. Then repartition your old disk to match
the new one, and hot add it to the RAID as the second disk (the same
process you'd use to replace a disk that had failed). The RAID layer
will sync from the new disk to the old, and then you'll have a fully
working two disk RAID mirror.

Ewan