[lug] Identical UUID for MD devices?

[Rob Nagler]

I think "cryptsetup remove" doesn't actually wipe the UUID from the crypt
header. I shredded the first few gigabytes, and the UUIDs are not there any
more after recreating the MDs:

NAME                                            MAJ:MIN RM   SIZE RO TYPE
MOUNTPOINT UUID
sda                                               8:0    0   7.3T  0 disk
           1e921f83-69c7-627a-523c-4bdb9d9e6a78
└─md3                                             9:3    0   7.3T  0 raid1
sdb                                               8:16   0   7.3T  0 disk
           1e921f83-69c7-627a-523c-4bdb9d9e6a78
└─md3                                             9:3    0   7.3T  0 raid1
sdc                                               8:32   0   7.3T  0 disk
           7d1b3ba9-16f2-0c84-79a2-f3801f6172ea
└─md4                                             9:4    0   7.3T  0 raid1
sdd                                               8:48   0   7.3T  0 disk
           7d1b3ba9-16f2-0c84-79a2-f3801f6172ea
└─md4                                             9:4    0   7.3T  0 raid1

BTW, this is something I didn't know. There's no way to span disks with
RAID1 with mdadm, e.g. this just creates four copies of the same data:

mdadm --create --metadata 1.2 --verbose /dev/md/3 --level=1
--raid-devices=4 /dev/sda /dev/sdb /dev/sdc /dev/sdd

You have to use RAID10 to span disks, but that's not what I want for this
application.

Rob
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