[arch-general] Why does newly created raid1 array not have /dev/disk/by-uuid entry?

[David C. Rankin]

All,

  I created GPT partitions on a pair of new 3T drives configured in raid1 as md4
on my system, e.g.:

 # cat /proc/mdstat
Personalities : [raid1]
md4 : active raid1 sdd[1] sdc[0]
      2930135488 blocks super 1.2 [2/2] [UU]
      [=>...................]  resync =  5.3% (157758400/2930135488)
finish=235.0min speed=196538K/sec
      bitmap: 21/22 pages [84KB], 65536KB chunk

md0 : active raid1 sdb5[1] sda5[0]
      511680 blocks super 1.2 [2/2] [UU]

md2 : active raid1 sda7[0] sdb7[1]
      921030656 blocks super 1.2 [2/2] [UU]
      bitmap: 0/7 pages [0KB], 65536KB chunk

md1 : active raid1 sdb6[1] sda6[0]
      52396032 blocks super 1.2 [2/2] [UU]

md3 : active raid1 sda8[0] sdb8[1]
      2115584 blocks super 1.2 [2/2] [UU]

unused devices: <none>

  Then 'mdadm --detail --scan' finds the UUID for the array, e.g.:

 # mdadm --detail --scan
ARRAY /dev/md3 metadata=1.2 name=archiso:3 UUID=8b37af66:b34403aa:fa4ce6f1:5eb4b7c8
ARRAY /dev/md1 metadata=1.2 name=archiso:1 UUID=62b42a42:c8b4eed1:295864d2:f815b367
ARRAY /dev/md2 metadata=1.2 name=archiso:2 UUID=73a0a0b5:fa3629e1:7c1a7c87:23044fc8
ARRAY /dev/md0 metadata=1.2 name=archiso:0 UUID=04940526:cfa6af2b:72c234e2:a987a858
ARRAY /dev/md4 metadata=1.2 name=valkyrie:4 UUID=6e520607:f152d8b9:dd2a3bec:5f9dc875


  I updated /etc/mdadm.conf with that information and was then going to do the
same for /etc/fstab. Before doing so, I thought I would confirm the UUID in
/dev/disk/by-uuid,

 # l /dev/disk/by-uuid/
lrwxrwxrwx 1 root root   9 Mar 19 16:41 3c0d11b5-c637-4def-a6e0-f48a4a17e71a ->
../../md0
lrwxrwxrwx 1 root root   9 Mar 19 16:41 402a70c8-b51b-41a0-aa88-3aa37c8dd6fd ->
../../md2
lrwxrwxrwx 1 root root   9 Mar 19 16:41 515ef9dc-769f-4548-9a08-3a92fa83d86b ->
../../md1
lrwxrwxrwx 1 root root   9 Mar 19 16:41 8920ca3f-f253-4011-9c9e-a6be513527e0 ->
../../md3


  Huh? No UUID for /dev/md4? Does it just not show up until the next boot? What
gives?

-- 
David C. Rankin, J.D.,P.E.