Arg: no mdadm on Ubuntu 18.04.5 Desktop install disk?

[Liam Proven]

On Sun, 3 Jan 2021 at 11:44, Patrick Irvine <pirv at cybersites.ca> wrote:
>
> Just some 2 cents, but I know that LVM has MDRAID embedded in it.  I
> wonder if MDRAID was dropped in favour of using LVM RAID?

No, it doesn't. This is wrong.

mdraid is entirely separate and distinct from LVM. You can build a
RAID volume from MDRAID and then put LVM on top of it and build an
encrypted filesystem in it, for instance.

LVM can build multi-drive volumes, including with redundancy, but that
is not the same thing at all.

Btrfs can do that as well, and you can also put Btrfs on top of LVM if
you wish. And put that on top of mdraid. They are all different and
independent.

This overlap is very confusing and I can see it's got you. No blame
there. It is hard to track.

This is why Ubuntu has gone with ZFS: ZFS includes the functionality
of mdraid, _and_ of LVM, _and_ of Btrfs, all in one single tool. I
have tried it and I am running it on a RasPi server that's blinking
away behind me right now. It is really very much easier than, say,
Btrfs or LVM.

I built a 5-drive ZRAID, formatted it and mounted it in a single
command. (I did have to write partition tables to the drives first,
but it was still hugely easier than doing it with mdraid etc.)

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