A couple of things i have set up for. The initital install is on LVM already so most of that was in place (including /) and i have no data on this. so if it wrecked its only an install away to start over.

But this is a good start for some reading, thank you!

On Thu, Jul 23, 2015 at 9:12 AM, Matt Graham <mhgraham@crow202.org> wrote:
On 2015-07-21 13:28, Stephen Partington wrote:
Ubuntu 15.04 installed and am looking to find out if there is a way
to migrate to raid on a running system.

In theory i should be able to do this by creating a degraded portion
of the raid volume on the empty disk, extend/move my LVM to that disk
then rebuild the original disk as part of that raid volume.

 This is a softRAID-1, right?  That makes the most sense for what you've said.

I was wondering if anyone had some documentation of information i
could read about this scenario.

 I did something like this when I moved my stuff from just 1 disk on regular partitions to softRAID-1.  First, back up all your junk, because there are multiple points in this where you could scribble all over your disks.  Second, make sure you have a LiveCD or LiveUSB disk to boot from if the bootloader goes wonky.  https://wiki.gentoo.org/wiki/Complete_Handbook/Software_RAID should be pretty applicable to working with softRAID and applicable to distros that are not Gentoo.

You'd first take the new disk and partition it.  I would think you'd need at least 2 partitions since having /boot on LVM is not going to work, and possibly 3 because having / on LVM has more fiddly bits than having it on a regular partition.

So, fdisk /dev/sdb , set it up with 2 or 3 partitions (whichever), and then set up the RAID.  This'll assume that your largest partition (the one that'll be your PV) is /dev/sdb2 .  You'd then do

mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb2 missing

This'll set up an array in degraded mode on /dev/md0.  You'd then pvcreate /dev/md0 , then vgextend $VG_NAME /dev/md0 , then pvmove /dev/$OLD_PV_LOCATION .  Then vgreduce $VG_NAME /dev/$OLD_PV_LOCATION  and pvremove /dev/$OLD_PV_LOCATION to remove the old PV from lvm's config.  Then you'd add the old PV back to the md0 with mdadm /dev/md0 --add /dev/$OLD_PV_LOCATION .  The disk sync will probably take a while.

You'll have to set things up so that the bootloader can figure everything out.  Are you going to put / on LVM?  That requires that the initrd have all the LVM tools on it.  I don't know if Ubuntu can handle that automatically or not--I would guess so, but ICBW.

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