raid1 will not work when I physically remove "removed" disk in Ubuntu 18.04

Question

/dev/sdc1 and /dev/sdd1 is raided (RAID1) into /dev/md3. /dev/md3 is encrypted with luksSetup.

Last night I got DegradedArray events for /dev/sdc1. I shutdown the system, physically removed the disk, and booted back up again. Now there is no md3 according to /proc/mdstat

$ mdadm --detail /dev/md3

Working Devices : 1 Failed Devices : 0 Spare Devices : 0

Consistency Policy : resync

 Name : xxx:3 UUID : 651393c9:1718e07a:6545908f:17100fe6 Events : 11103 Number Major Minor RaidDevice State - 0 0 0 removed 1 8 49 1 active sync /dev/sdd1 

The physically remaining disk (the working one) is now called /dev/sdc. The partition type of /dev/sdc1 is "Linux RAID autodetect". I cannot open this with luksOpen, it doesn't even ask for password.

How can I physically remove the broken disk and keep using the working one? Right now I must keep the broken disk physically connected to the server to be able to continue using the working one.

Answer 1

Make sure that grub is installed on the second drive and switch your BIOS settings to boot from active disk.

You can install GRUB with:

sudo grub-install /dev/sdd sudo update-grub2