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I have a home server running 10.04 configured with an mdadm-based RAID array. The boot and /home partitions are both on RAID-1 arrays, and I have a large data partition on RAID-5. There are three disks, with a partition from each disk making up each mdadm array--so three arrays (two RAID-1, one RAID-5), each with three disks, /dev/sda, sdb, and sdc.

Recently, /dev/sda failed, and mdadm kicked it out of the array correctly. I replaced the drive, and am now trying to boot, but when I do, I get an error "Reboot and Select proper Boot device or Insert Boot Media in selected Boot device and press a key." It seems that this is likely a message from my ASUS BIOS.

It seems to me that this is likely due to a missing boot loader. Am I correct in this? I'm guessing that since /dev/sda is likely what the system is trying to boot off of and since it is now a blank drive until I can boot to rebuild the array, that the machine can't boot. Oddly, I swear I remember installing GRUB to all of the disks and making sure they were bootable.

I'm tempted to change the boot order in the BIOS and see if that works, but I'm worried that doing this might somehow corrupt the now degraded RAID-5 partition (not sure why... but I'd rather not do something I don't fully understand the implications of).

How should I go about fixing this? Any help is greatly appreciated.

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Yes, it sounds like your BIOS is trying to boot from the first drive and not finding a boot record.

If you tell it to try booting from another drive instead, and it works, you can always break into the grub menu well before anything will try writing to any disk (you probably have the menu hidden - hold SHIFT to reach it).

Alternatively, you can boot off a live CD if you have one, and setup the boot record on sda from there.

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Thanks! What would be the best way to go about doing this? Is there some way to copy the boot record from one of the working hard drives? I just want to make sure I don't botch the RAID-5 array. –  aravenel Feb 18 '12 at 0:26
    
Turns out this fixed it--I forced the BIOS to boot from sdb, and it booted fine. Then rebuilt the array and reinstalled GRUB to sda. Thanks! –  aravenel Feb 18 '12 at 5:08
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