On Sun Jan 19, 2020 at 11:02:54AM -0600, William Morgan wrote:

bill@bill-desk:~$ sudo lsblk -f
NAME    FSTYPE            LABEL       UUID
    FSAVAIL FSUSE% MOUNTPOINT
.
.
.
sdj
└─sdj1  linux_raid_member bill-desk:0
06ad8de5-3a7a-15ad-8811-6f44fcdee150
  └─md0 ext4
ceef50e9-afdd-4903-899d-1ad05a0780e0
sdk
└─sdk1  linux_raid_member bill-desk:0
06ad8de5-3a7a-15ad-8811-6f44fcdee150
  └─md0 ext4
ceef50e9-afdd-4903-899d-1ad05a0780e0
sdl
└─sdl1  linux_raid_member bill-desk:0
06ad8de5-3a7a-15ad-8811-6f44fcdee150
  └─md0 ext4
ceef50e9-afdd-4903-899d-1ad05a0780e0
sdm
└─sdm1  linux_raid_member bill-desk:0
06ad8de5-3a7a-15ad-8811-6f44fcdee150
  └─md0 ext4                          ceef50e9-afdd-4903-899d-1ad05a0780e0

But then I get confused about the UUIDs. I'm trying to automount the
array using fstab (no unusual settings in there, just defaults), but
I'm not sure which of the two UUIDs above to use. So I look at mdadm
for help:

bill@bill-desk:~$ sudo mdadm --examine --scan
ARRAY /dev/md/0  metadata=1.2 UUID=06ad8de5:3a7a15ad:88116f44:fcdee150
name=bill-desk:0

However, if I use this UUID starting with "06ad", then I get an error:

bill@bill-desk:~$ sudo mount -all
mount: /media/bill/STUFF: mount(2) system call failed: Structure needs cleaning.

But I don't know how to clean it if fsck says it's OK.

On the other hand, if I use the UUID above starting with "ceef", then
it mounts and everything seems OK.

Basically, I don't understand why lsblk lists two UUIDs for the array,
and why mdadm gives the wrong one in terms of mounting. This is where
I was confused before about the UUID changing. Any insight here?

One is the UUID for the array (starting with "06ad") - this is what you
use in /etc/mdadm.conf. The second is the UUID for the filesystem you
have on the array (starting with "ceef") - that's used in /etc/fstab. If
you recreate the filesystem then you'll get a different filesystem UUID
but keep the same array UUID.

Cheers,
    Robin
-- 
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    ( ' }     |       Robin Hill        [off-list ref] |
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