LVM and raid

[Stephen Partington]

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 at 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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-- 
A mouse trap, placed on top of your alarm clock, will prevent you from
rolling over and going back to sleep after you hit the snooze button.

Stephen
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