Recover encrypted MD RAID1 member

"Brian J. Murrell" <[email protected]> Mon, 02 Dec 2024 08:45:41 -0500

Newsgroups	dev.linux.lists.cryptsetup
Message-ID	<[email protected]>

I was doing some maintenance of my RAID1 array and something seems to
have gone sideways.  The array's structure looks like this:

sdb                                            8:16   0   3.7T  0 disk
└─md0                                          9:0    0   3.7T  0 raid1
  └─md0_encrypted                            253:39   0   3.7T  0 crypt
    └─backups-backups                        253:40   0     3T  0 lvm 
sdd                                            8:48   0   3.7T  0 disk
└─md0                                          9:0    0   3.7T  0 raid1
  └─md0_encrypted                            253:39   0   3.7T  0 crypt
    └─backups-backups                        253:40   0     3T  0 lvm 
sde                                            8:64   0   3.7T  0 disk
└─md0                                          9:0    0   3.7T  0 raid1
  └─md0_encrypted                            253:39   0   3.7T  0 crypt
    └─backups-backups                        253:40   0     3T  0 lvm 

Except that sdd is not actually active in the array as in the failed
state:

Personalities : [raid1] 
md0 : active raid1 sdb[5] sde[3] sdd[4](F)
      3906854744 blocks super 1.2 [3/2] [_UU]
      bitmap: 14/15 pages [56KB], 131072KB chunk

unused devices: <none>

I think sdd was removed before things went sideways and so sdd might be
my only good copy of the array.

The question is, how can I work with it independently of the array now?
I'd like to get to the point of being able to check the content of
backups-backups filesystem on that single disk, again, independently of
the existing md0 array.

I know there is some crossover between LUKS and MD here, but I am
suspecting that the LUKS part here is going to be the more complicated
part and I am pretty green with regard to LUKS so hoping for some help
in that regard.

Any help or suggestions would be much appreciated.

Cheers,
b.

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