Hi!

I originally had a software RAID-1 setup with two disk. Unfortunately, I discovered (too late) that GRUB was not configured properly and was only booting off of the first disk, hd0 (i.e. /dev/sda). Guess which disk failed on me?

I fixed the above mess, and now I want to add a third drive, /dev/sdc, to my working software RAID-1 as a spare. Please give me a sanity check on this as well as telling me if I added extra steps that are not needed:

First I copied the partition table to my new drive:
sfdisk -d /dev/sda | sfdisk /dev/sdc

This gave me /dev/sdc1 as type fd (Linux raid autodetect).

I then added /dev/sdc1 to my raid:
mdadm --add /dev/md0 /dev/sdc1

I look at /proc/mdstat and see sdc1[2](S) meaning that the spare has been added.

Finally, I create a new /etc/mdadm.conf using:
mdadm --examine --scan > /etc/mdadm.conf

Now to deal with GRUB. I want to be able to boot off of any of the three disks that are now in my software RAID-1. After editting, the top of my /boot/grub/menu.1st file has:
default=0
fallback=1 2
timeout=5

I also added a third kernel stanza by copying the previous stanza and changing the root line to read:
root (hd2,0)

Finally, I generated a new ramdisk using:
mkinitrd /boot/initrd-`uname -r`.img `uname -r`

Before adding the spare, I installed the GRUB bootloader on the first and second drives, hd0 and hd1 respectively.

Do I need to install the bootloader on the spare as well or will that be copied if the spare is activated and the array is rebuilt? Is there anything else I need to do?

Thanks!

You need to copy/install the bootloader to the spare; the RAID portion of the drive is only the FD partition, while the bootloader is (typically) in the MBR.

I see. I wasn't sure if the mechanism that brings the two disks into sync in a mirrored array would handle the MBR. I discovered that the device had to be formatted before it could successfully run the setup command under the GRUB shell. In order to format, I had to remove the device from the array (no need to fail the device first since it was a spare) first.

Every thing seems to be fine now. Hopefully the array will gracefully survive the next drive failure.

Thanks for the help!

Way you need the new ramdisk?