[olug] Mirroring a boot drive

Justin Reiners justin at hotlinesinc.com
Thu Sep 27 09:02:59 CDT 2018

On Thu, Sep 27, 2018 at 8:40 AM Ben Hollingsworth <obiwan at jedi.com> wrote:

> On 09/27/2018 08:02 AM, Justin Reiners wrote:
> > Periodically dd your drive and compress it to another location, then you
> > can just dd it to a new drive the same or larger in size.
> Yes, but will that overwrite any of the RAID config that's needed for
> the mirrored boot?  Probably.  I need to know what must be preserved /
> merged vs overwritten.
> Writing dd data to a hardware raid will not overwrite the data. Software
raid it would for sure.

> > Honestly, I'm not sure the best way to do it from a live system, it's
> been
> > a long time since I have used software raid, everything I have has a raid
> > card onboard.
> The system doesn't have to be live.  I can take it down for an evening &
> run off a live USB stick to do the switch.

By live system, I mean one someone has lived in. I do see instructions for
software raid here:
but honestly if you do not need raid the best bet would be a couple cron
scripts to back up the partition or drive, and restores should always work
with dd and a single drive. I've done it for years now.
I'm mainly a hardware raid guy, I'm a sysadmin with a bunch of poweredge
hardware so the raid cards take care of setting up the raid, and I just
dump data back onto the array once it's built. I can also just pull a bad
drive and replace it and it happily rebuilds without having to do anything
on the OS itself. Some motherboards also have this functionality.

Just make sure you take a backup before you start messing with adding or
removing raid. A rebuild of the host is always better imo because you also
have a solid backup, which raid is not. Is it a production setup or homelab?

> > I remember horror stories of software raid screwing up when we used it,
> not
> > being able to replace drives, no documentation, and onsite helping hands
> > tech confusion.
> I've been using software RAID5 on my data filesystems for many years
> now, so I'm quite comfortable with managing it once it's running. I'm
> just not sure how to get Ubuntu to boot off a RAID1 (short of a fresh
> server install), and how to best get my current OS over to it.

I'm sure someone here knows the answer to this, I'm really out of touch
with mdadm anymore, even my home stuff has hardware raid, which I run a
RAID 10 on. Can't lose the movies :)

> > If I had to do it, I'd buy a pci express raid card, do a full backup,
> buy a
> > couple new SSDs and dd the info back on to the new raid,
> As long as I can get my mobo to boot off that card, I could do that.
> However, I've grown fond of the easy notifications & monitoring that
> software RAID provides.  I also want to run SMART tests on the
> individual disks.  I'm guessing I wouldn't get any of that with a
> hardware RAID card.  Am I wrong?
Hardware raid will flash a heath led on my stuff, and the dell software set
up properly can send notifications when things go bad. I'm pretty sure a
decent card would offer the same features, or you could roll your own.

> > On Wed, Sep 26, 2018 at 10:40 PM Ben Hollingsworth <obiwan at jedi.com>
> wrote:
> >
> >> I've got a Ubuntu system (currently 16.04, but soon 18.04) with a
> >> single, 5.5-yr-old SSD boot/root drive and a handful of other disks in a
> >> RAID5 data array.  I'd like to add a second boot drive to create a RAID1
> >> mirror, since the current boot drive won't last forever.
> >>
> >> There are plenty of instructions available for installing a fresh Ubuntu
> >> server install on a RAID1 partition.  However, I need to keep & upgrade
> >> my existing install, since it's heavily customized.  I can't find any
> >> instructions specifically for this scenario.  Have any of you ever done
> >> this?
> >>
> >> The idea I've had is to install the new disk and unplug the existing
> >> boot disk.  Install a fresh 18.04 server release using the new disk and
> >> some spare space from another old disk as the mirrored pair. Once that's
> >> running, copy the old boot drive's data on top of the new boot drive
> >> (this is the part I'm not sure will work well).  Once the new
> >> drive/mirror is set up with my old OS, remove the old spare drive from
> >> the mirror and replace it with the old boot drive.  Yes, I have multiple
> >> backups.
> >>
> >> Does that sound plausible?  Is there a better way?
> >>
> >> I suppose the alternative is to just keep running off a single drive,
> >> and replace the old one as soon as it throws the first SMART error.
> >> That makes me nervous, though.
> --
> *Ben "Obi-Wan" Hollingsworth* obiwan at jedi.com <mailto:obiwan at jedi.com>
> www.Jedi.com <http://www.jedi.com>
> The stuff of earth competes for the allegiance I owe only to the
> Giver of all good things, so if I stand, let me stand on the
> promise that You will pull me through. /-- Rich Mullins/
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