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

On Mon, Jun 22, 2026 at 07:50:10AM +0200, Michel Verdier wrote:
> On 2026-06-21, Paul Leiber wrote:
> 
> > I managed to rebuild the md RAID1 using the data on the seemingly failed
> > device (partition_1). First, I did a dd dump of partition_2 (currently in
> > usage) in order not to lose data. Then, I recreated the RAID1 using the data
> > from partition_1:
> >
> > mdadm --stop /dev/md0 # This stops the degraded RAID1
> > mdadm --assemble --update=uuid /dev/md0 /dev/mapper/partition_1 # This creates a new RAID1 using the partition_1, a new array UUID is required in order for --assembly to work
> > mdadm --manage --add /dev/md0 /dev/mapper/partition_2 # This adds partition_2 to the RAID1, contents of partition_1 are replicated to partition_2 automatically
> 
> Your commands are strange : the partitions should be the disk partitions
> from /dev and not mapped ones. Or you have another layer ? From where
> come /dev/mapper/partition_1 and /dev/mapper/partition_2 ?

If I have been following along, the RAID parts are LUKS encrypted devices,
so to me it does make sense.

Cheers
-- 
t

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

iF0EABECAB0WIQRp53liolZD6iXhAoIFyCz1etHaRgUCajjPtwAKCRAFyCz1etHa
Rh7cAJ4vPPLY7ZvDJaDd59/5xglbU7pWfQCeMVBEh+/YSvlyewXnX0FoZGvOfwg=
=ofKO
-----END PGP SIGNATURE-----