[lug] Identical UUID for MD devices?

[Rob Nagler]

I created two RAID1 devices with mdadm, but the UUIDs are identical (see
below). I actually created and destroyed an array with all four disks,
wiped the signatures, and then recreated the arrays as separate mirrored
disks. I'm going to recreate the arrays, but I was wondering if someone had
seen this before. Thanks, Rob

# lsblk -o +UUID
NAME                                            MAJ:MIN RM   SIZE RO TYPE
MOUNTPOINT UUID
sda                                               8:0    0   7.3T  0 disk
           a0793173-d347-8d42-4b5b-8ae915570d5e
└─md3                                             9:3    0   7.3T  0 raid1
          *38bc1e03-f953-4104-84b4-fbf78b5895d4*
sdb                                               8:16   0   7.3T  0 disk
           a0793173-d347-8d42-4b5b-8ae915570d5e
└─md3                                             9:3    0   7.3T  0 raid1
          *38bc1e03-f953-4104-84b4-fbf78b5895d4*
sdc                                               8:32   0   7.3T  0 disk
           f6f1266c-1f97-4ff8-f142-6979a84ba08a
└─md4                                             9:4    0   7.3T  0 raid1
          *38bc1e03-f953-4104-84b4-fbf78b5895d4*
sdd                                               8:48   0   7.3T  0 disk
           f6f1266c-1f97-4ff8-f142-6979a84ba08a
└─md4                                             9:4    0   7.3T  0 raid1
          *38bc1e03-f953-4104-84b4-fbf78b5895d4*
sde                                               8:64   0 238.5G  0 disk
├─sde1                                            8:65   0     1G  0 part
           97e01b29-f07f-5064-040c-4a2620141498
│ └─md0                                           9:0    0  1023M  0 raid1
/boot      b35251df-1483-4b5d-8c5a-d2d4cd72091d
└─sde2                                            8:66   0 237.5G  0 part
           c73e71b6-e620-2f74-3c77-d0f423ee9247
  └─md2                                           9:2    0 237.4G  0 raid1
          e1f57619-ef51-48f4-bab6-fd080522cd68
    └─luks-e1f57619-ef51-48f4-bab6-fd080522cd68 253:0    0 237.4G  0 crypt
          aqyS9B-z8kQ-GYeA-OaQF-s1Ux-DnAy-3ucPpN
      └─centos-root                             253:1    0     5G  0 lvm
 /          518ac627-bc81-4ea7-9df2-b84b43c2e90f
sdf                                               8:80   0 238.5G  0 disk
├─sdf1                                            8:81   0     1G  0 part
           97e01b29-f07f-5064-040c-4a2620141498
│ └─md0                                           9:0    0  1023M  0 raid1
/boot      b35251df-1483-4b5d-8c5a-d2d4cd72091d
└─sdf2                                            8:82   0 237.5G  0 part
           c73e71b6-e620-2f74-3c77-d0f423ee9247
  └─md2                                           9:2    0 237.4G  0 raid1
          e1f57619-ef51-48f4-bab6-fd080522cd68
    └─luks-e1f57619-ef51-48f4-bab6-fd080522cd68 253:0    0 237.4G  0 crypt
          aqyS9B-z8kQ-GYeA-OaQF-s1Ux-DnAy-3ucPpN
      └─centos-root                             253:1    0     5G  0 lvm
 /          518ac627-bc81-4ea7-9df2-b84b43c2e90f
# ls -1 /dev/disk/by-uuid/
*38bc1e03-f953-4104-84b4-fbf78b5895d4*
518ac627-bc81-4ea7-9df2-b84b43c2e90f
b35251df-1483-4b5d-8c5a-d2d4cd72091d
e1f57619-ef51-48f4-bab6-fd080522cd68
# mdadm --detail /dev/md/3
/dev/md/3:
           Version : 1.2
     Creation Time : Thu Feb  8 15:29:12 2018
        Raid Level : raid1
        Array Size : 7813895488 (7451.91 GiB 8001.43 GB)
     Used Dev Size : 7813895488 (7451.91 GiB 8001.43 GB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Thu Feb  8 16:21:11 2018
             State : clean, resyncing
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : bitmap

     Resync Status : 5% complete

              Name : localhost.localdomain:3  (local to host
localhost.localdomain)
              UUID : a0793173:d3478d42:4b5b8ae9:15570d5e
            Events : 491

    Number   Major   Minor   RaidDevice State
       0       8        0        0      active sync   /dev/sda
       1       8       16        1      active sync   /dev/sdb
# mdadm --detail /dev/md/4
/dev/md/4:
           Version : 1.2
     Creation Time : Thu Feb  8 15:29:28 2018
        Raid Level : raid1
        Array Size : 7813895488 (7451.91 GiB 8001.43 GB)
     Used Dev Size : 7813895488 (7451.91 GiB 8001.43 GB)
      Raid Devices : 2
     Total Devices : 2
       Persistence : Superblock is persistent

     Intent Bitmap : Internal

       Update Time : Thu Feb  8 16:21:31 2018
             State : clean, resyncing
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : bitmap

     Resync Status : 5% complete

              Name : localhost.localdomain:4  (local to host
localhost.localdomain)
              UUID : f6f1266c:1f974ff8:f1426979:a84ba08a
            Events : 491

    Number   Major   Minor   RaidDevice State
       0       8       32        0      active sync   /dev/sdc
       1       8       48        1      active sync   /dev/sdd
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