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.