If MBR is broken, how to fix on RAID + LUKS encryption?

Question

Problem: After HDD failure in a Software-Raid Mirror Debian does not boot. Only black screen with blinking _

Debian Setup:
Within the raid I have a complete system encryption with luks.

I am not 100% sure if the MBR is broken or missing or what causes the problem. Usually before the disk failure the PC did boot and I had to enter the passphrase for the encryption and the pc would boot.

Current status:
I mounted the raid/luks manually and copied all data. So the data is secure.

What I want to do:

(#1 prefered) I would like to find the problem (repair MBR ?). Boot the pc. Add the new HDD to my raid and finish.

(or #2 if #1 does not work) Since data is secure setting up a new system.

Answer 1

I rescued the bootloader using the following commands:

1. Booted from linuxmint disc ISO
2. Installed mdadm

3. Added raids:

   mdadm -A -R /dev/md0 /dev/sdb1
   mdadm -A -R /dev/md1 /dev/sdb2
   

   I have separate boot partition on sdb1|md0

4. Unlock the encrypted partition (sdb1|md0 is not encrypted)

   cryptsetup -v luksOpen /dev/md1 rescuedata
   

5. Mounted the volume groups which appear now at /dev/mapper/vg.VOLGROUPNAME:

   mount /dev/mapper/vg.VOLGROUPNAME /mnt  
   mount /dev/md0 /mnt/boot  
   mount --bind /dev /mnt/dev
   

6. Got into chroot environment and installed grub:

   chroot /mnt  
   /usr/sbin/grub-install --recheck /dev/sdb
   

7. Reboot & happy