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I recently set up a NAS server running a Debian OS (6.0.4)

It contains 4 disks, 3 of them are in a Raid5 array, while the last one is used for the OS.

To simulate a disk-failure I unplugged one of the raid disks, which resulted in the OS being unable to boot.

It started the boot, recognized that md0 (the raid array) was running on 2/3 disks, and then threw a few errors.

It was unable to find the following directories:

/dev/root on /root,
/dev on /root/dev,
/sys on /root/sys,
/proc on /root/proc

It appears this happens regardless of which raid disk is removed. These directories are supposed to be on /dev/sdd my system disk.

Output from fstab and blkid : http://dl.dropbox.com/u/6017799/NASOutput.txt

If you need additional info, please let me know.

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"and then threw a few errors" - you should state what these errors are. Diagnostic messages are useful when trying to diagnose a problem! –  David Spillett Mar 13 '12 at 8:58
    
Sorry for not being specific - the errors it threw were "Directory not found" on the directories mentioned in the line below it. I'm guessing the only reason it didn't boot was due to not being able to find those –  Ronni Mar 13 '12 at 9:58
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2 Answers

You take a disk out, and then the system fails to boot beyond loading the kernel. Once the kernel tries to find the filesystems it complains and drops you to a minimal shell. If it's something like that, then it's likely that grub(2) is not finding the root disk device. Because you took out a disk the device names have changed, what once was /dev/sdd could now be /dev/sdc.

It's possible you need to reconfigure grub(2) to use UUIDs instead of device names.

Although this seems at least a bit weird:

It was unable to find the following directories. /dev/root on /root, /dev on /root/dev, /sys on /root/sys, /proc on /root/proc

Why would these directories be in the root home directory? Those normally would be directly located on / (/dev et al). Did you create symlinks from /dev to /root/dev? if so, why?

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I haven't created any symlinks to those directories, nor are they shown when i enter /root and look for them - not sure what that's all about :/ I suppose grub might be the reason behind it, so I'll try to investigate how to switch it to using UUIDs. –  Ronni Mar 14 '12 at 7:49
    
My grub2 .cfg file - it seems to be already implementing UUID? dl.dropbox.com/u/6017799/Grubcfg.txt –  Ronni Mar 14 '12 at 7:57
    
It's set in /etc/default/grub, could you show contents of that file? –  aseq Mar 14 '12 at 22:03
    
    
That looks fine, could you boot with a debian CD in rescue mode? Then choose the option to execute a shell in your systems root filesystem. Maybe you need to mount places such as /usr and /var. Then run "upgrade-from-grub-legacy", select your boot device (should be something like /dev/sdx, not a partition). When it's finished and reported no errors try a reboot. If it can't find the grub command you may have to source your .profile or .bash_profile in the /root (i.e. root's $HOME, command: source /root/.profile etc.). –  aseq Mar 15 '12 at 19:36
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Adding another answer because the discussion gets quite long.

I am still wondering about

It was unable to find the following directories:

/dev/root on /root,

/dev on /root/dev,

/sys on /root/sys,

/proc on /root/proc

Why do you say /root/dev etc? Are you just writing /root to indicate the root filesystem? That's something different than /root which is the home directory of the root account.

/dev, /sys and /proc should NOT be in /root.

If possible could you paste text or take a screenshot of the actual screen where the boot fails? So we can see more of the errors.

Update: Something must have caused your system to attempt to mount /proc, /dev/, /sys at the wrong place. You have to find out why. Do a "grep mount /etc/init.d" and carefully check the scripts it returns. In addition look at anything else /etc that might make your system mount these filesystems in the wrong place.

You have to find out why your systyem tries to mount these filesystems in /root and fix that

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I'll add a screenshot once I get home - the directory it indicates the problem on is /root though (the home dir of Root) –  Ronni Mar 20 '12 at 9:26
    
dl.dropbox.com/u/6017799/IMG_0075.JPG This is a link of the specific error during boot. –  Ronni Mar 27 '12 at 9:10
    
See my updated answer. –  aseq Mar 27 '12 at 19:08
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