Re: How to salvage a degraded mdadm RAID1 with as little data loss as possible?

On Tue, Jun 23, 2026 at 08:28:50AM +0200, Michel Verdier wrote:
> On 2026-06-22, Paul Leiber wrote:
> 
> >>> RAID is always before LUKS : partition > RAID array > LUKS > filesystem
> >> "Is always" means for you "should always be" or "has to be"?
> >>
> >> As far as I understand OP, their case is the other way around (and I don't
> >> see why it shouldn't be technically possible: a block device is a block
> >> device is a block device, after all).
> >
> > Tomas' description of my setup is correct, LUKS before RAID. It has
> > been working in the past, and it is working right now again. Is this
> > type of setup recommended? I don't know. BTRFS doesn't show any issues
> > with this setup.
> 
> So Tomas found your problem. It is at best useless to have 
> partition > LUKS > RAID array > filesystem

I strongly disagree here.

> I cannot see how it managed to work. It suppose the 2 LUKS are identical
> which is a nonsense. Also a small change in data gives a bigger change in
> a LUKS partition thus bigger to sync. I don't know enough about LUKS but
> I suppose you loose LUKS atomicity during sync.

Not the LUKS are identical. Their decrypted layers are, ideally. Of
course this costs additional processing power (you have to de-/encrypt
things twice), and I don't (yet) see an advantage to this scheme, but
it is definitely feasible.

Cheers
-- 
t

-----BEGIN PGP SIGNATURE-----

iF0EABECAB0WIQRp53liolZD6iXhAoIFyCz1etHaRgUCajpFTAAKCRAFyCz1etHa
Ri10AJ0Wsco8BRy94JbpiXT64rNkUJWTAwCeOo3dqGDzc/E6oyaM5m/LQdBZAr0=
=fa8z
-----END PGP SIGNATURE-----