I think you've covered all the bases.

When in the recovery environment, all you really need to do is create the correct partition structure on the new drive and install GRUB.

Well, you may also want to start the rebuild process for the partition containing /boot, and wait for it to complete. I don't know how smart GRUB is when it comes to loading the kernel and initrd from a degraded mdadm RAID volume.

Once GRUB is in place, you can safely reboot the server and then perform the remaining tasks.

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I did run some extra commands to find out the location of grub.

GRUB found

The above command tells us whether or not Grub is installed on a particular disk. In our case, I found out that Grub is installed on /dev/sdb. Is as well logical as this disk is a part of the software raid md0 (/boot). Does it mean, the system will be able to boot *normally* even if we restart the system without taking out the faulty disk.

This question is only for knowledge purpose!!!

In order for the system to be able to boot from the second drive (using GRUB), the GRUB bootblock must be installed, it must be able to locate the 2. stage bootloader, and of course the BIOS must be able to boot from the drive.

It seems there's indeed a GRUB bootblock present in the MBR of the second drive. Will it be able locate and load the bootloader if the first drive is missing or non-functional? I can't say. In theory it should, given that is supposedly supports software RAID volumes.

If the first drive has bad blocks, the very minimal loader in the bootblock must contain functionality to handle a case where the bootblock is loaded from drive A, but the second stage loader must be fetched from drive B due to read errors on drive A. Perhaps I'm being overly pessimistic, but I have my doubts that the tiny MBR bootloader contains such functionality.

On the other hand, if the first drive is missing entirely, what used to be the second drive (BIOS drive 0x81) will automatically become the first drive (BIOS drive 0x80). If the MBR loader simply keeps using the same BIOS drive that was used to load the MBR in the first place, the system will probably boot normally.

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