Re: [PLUG] RAID-1 mdadm vs. Mobo H/W = moot

[Keith via plug <plug@lists.phillylinux.org>]

On 7/20/20 9:24 AM, K.S. Bhaskar via plug wrote:

On Mon, Jul 20, 2020 at 2:47 AM JP Vossen via plug <plug@lists.phillylinux.org> wrote:

On 7/16/20 9:21 PM, JP Vossen wrote:
> I'm building 2 new PCs and I am wondering about RAID-1.  I've been using
> mdadm RAID-1 for at least a decade with excellent results.  But I
> haven't had to deal with (U)EFI up to now, and that's a mess, along with
> the fact that the Linux Mint/Ubuntu `Ubiquity` installer doesn't do
> RAID.  :-(
>
> I only care about RAID-1 (mirror) and Linux.  I would not even consider
> Mobo RAID anymore more complicated than a mirror, but since a mirror is
> *so* simple...
<snip>

The short version is, the Asus ROG STRIX B450-F GAMING ATX AM4
motherboard [0] is *not* capable of using both M2 slots if you are
*also* using the Radeon Vega Graphics processor [1]! :-(

So we fell back to plan-b which is to install some old HDD drives I had
laying around and I'll get around to writing some kind of `rsync` script
(after I take a look at Brent's code).

Thanks for the thoughts, I was reasonably certain about not doing the
hardware RAID, and that was certainly confirmed!

[KSB] <…snip…>

Bhaskar, I recall you've talked about your /spare/ process before.  I
think perhaps some of my concerns with mobo H/W RAID came from similar
discussions with you and/or wider PLUG.  Plan B is going to be similar,
but actually a bit simpler.

nvme0n1p2 is the main storage.  sda1 *will be* a periodic `rsync` clone
of nvme0n1p2, with some hack I haven't figured out yet for the
`/data/etc/fstab`.  It will also house Mint's "TimeShift" (think Mac
Time Machine).  So if nvme0n1p2 unexpectedly dies [2], I can just boot
from sda and keep going, possibly with having to do a bit of a restore
from either TimeShift or my other backups.

[KSB] I confess that I don't know as much about DRBD as I could or should, but I wonder if it might be possible to use it to replicate from the NVMe storage to the old HDD. This would also avoid the need to hack on /etc/fstab or /boot/grub/grub.cfg – since the HDD partition would not need to be mounted, it can have the same UUID as the NVMe partition. Before doing something “risky” shut down the DRBD replication, and start it up again once the upgrade or whatever completes successfully.

DRBD is basically network RAID-1 so you wouldn't use it to mirror drives on the same system.  You **could** use it to replicate a system mirror set from server A to server B but personally, I don't think its worth it.  My current data protection solutions use DRBD and as much as I love it, when a full resync gets triggered having to scrub through and get the secondary up to date is nerve racking because you can't use the secondary until DRBD thinks its stable.  That's not as big a deal with you're on a LAN but actual RAID-1 will always let you mount the other mirror even if its out of date.

 -- 
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Keith C. Perry, MS E.E.
Managing Member, DAO Technologies LLC
(O) +1.215.525.4165 x2033
(M) +1.215.432.5167
www.daotechnologies.com
  

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