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OK... so I retried... Here is mdstat after installing and booting, and waiting to ensure all syncing had completed:
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md1 : active raid1 sda2[0] sdb2[1]
19529656 blocks super 1.2 [2/2] [UU]
md0 : active raid1 sda1[0] sdb1[1]
48826296 blocks super 1.2 [2/2] [UU]
md2 : active raid1 sda3[0] sdb3[1]
175779768 blocks super 1.2 [2/2] [UU]
unused devices: <none>
Next, I shut down the system and remove disk 1. On reboot, I run mdstat and note the degraded array with missing members:
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md1 : active (auto-read-only) raid1 sda2[0]
19529656 blocks super 1.2 [2/1] [U_]
md0 : active raid1 sda1[0]
48826296 blocks super 1.2 [2/1] [U_]
md2 : active raid1 sda3[0]
175779768 blocks super 1.2 [2/1] [U_]
unused devices: <none>
Then I shut down and re-insert drive 2:
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md1 : active raid1 sda2[0] sdb2[1]
19529656 blocks super 1.2 [2/2] [UU]
md0 : active raid1 sda1[0]
48826296 blocks super 1.2 [2/1] [U_]
md2 : active raid1 sda3[0]
175779768 blocks super 1.2 [2/1] [U_]
unused devices: <none>
Then I try manually adding the disks per the test case:
bladernr@ubuntu"~$ sudo mdadm --add /dev/md0 /dev/sdb1
mdadm: /dev/sdb1 reports being an active member for /dev/md0, but a --re-add fails.
mdadm: not performing --add as that would convert /dev/sdb1 in to a spare.
mdadm: To make this a spare, use "mdadm --zero-superblock /dev/sdb1" first.
bladernr@ubuntu:~$ sudo mdadm --re-add /dev/md0 /dev/sdb1
mdadm: --re-add for /dev/sdb1 to /dev/md0 is not possible.
I got the same for /dev/md2 when trying to re-add /dev/sdb3, so I zero the superblocks, which is essentially blanking the disk and adding it as though it were a brand new disk into the array.
bladernr@ubuntu"~$ sudo mdadm --zero-superblock /dev/sdb3
bladernr@ubuntu"~$ sudo mdadm --zero-superblock /dev/sdb1
bladernr@ubuntu"~$ sudo mdadm --add /dev/md0 /dev/sdb1
mdadm: added /dev/sdb1
bladernr@ubuntu"~$ sudo mdadm --add /dev/md2 /dev/sdb3
mdadm: added /dev/sdb3
bladernr@ubuntu:~$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md1 : active raid1 sda2[0] sdb2[1]
19529656 blocks super 1.2 [2/2] [UU]
md0 : active raid1 sdb1[2] sda1[0]
48826296 blocks super 1.2 [2/1] [U_]
[
md2 : active raid1 sdb3[2] sda3[0]
175779768 blocks super 1.2 [2/1] [U_]
unused devices: <none>
according to the test case, the most I should have to do is just plug the disk back in and reboot the server which should cause mdadm to automatically re-add the disk and start re-syncing. The most I should have to do is just use the --add command to add the disk back in (or re-add) manually.
What I am actually having to do is essentially destroy the partitions for the ext4 LUNs and add them back in as brand new disks. This again, did not happen to the SWAP md device which DID boot degraded, and then re-connected automatically when I put the disk back in.