LinuxQuestions.org - Superblock problems (I think)

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Superblock problems (I think)

Hi all, had a disk in a RAID 5 go bad yesterday. After I replaced the drive this morning, the system fails to boot. It's complaining about a bad magic number. From what I've read today, this should indicate a bad superblock. I tried to view backup superblocks with dumpe2fs | grep 'superblock' and was told bad magic number. To me, that doesn't sound promising. Attached are the results of an fdisk -l. Does the partition table look OK? Also, attached is the output from fsck /dev/sda4. it says "Attempt to read block from filesystem resulted in short read while trying to open /dev/sda4. Could this be a zero-length partition?"

This is a dell poweredge 1900. 3x500GB drives in a RAID 5. It was running CentOS 5.3.

Any help anyone can give to get it back up and running would be great. Yes, I have a backup, but it's online and there's about 400GB. I'd love to be able to dump at least some of the data to an external drive, if possible. Thanks!

Hi,
You may get a better answer from someone who knows more, but this is what I would try:
Get hold of a Live CD of a distro which uses Grub1 not Grub2 or Lilo. That means most distros.
Boot with it and get a root terminal. Type "grub" to get a grub prompt.
Then

Code:

root (hd0,2)

setup (hd0,2)

This will put Grub into the superblock of sda3. (I assume it is in sda3 that your linux lives)
If you then type

Code:

chainloader +1

boot

it ought to boot. If you get an error eg "File not found" or some such, try typing (from the grub prompt)

Code:

kernel /boot/vmlinu

and then hit the TAB key for autocompletion. Then type

Code:

initrd /boot/ini

and hit TAB again.Then type

Code:

boot

and it should boot.
If you have been using Grub1 to boot, it should be on the MBR. It may be corrupted,in which case from a grub prompt (either using your live CD or in a root terminal in linux), typing

Code:

root (hd0,2)

setup (hd0)

will put it into the MBR, overwriting whatever was there.
If you're with Grub2, then (from your installed linux), typing in a root terminal:

Code:

grub-install /dev/sda

update-grub

will install Grub2 into the MBR, overwriting whatever was there.
I think that the fsck message was probably normal, given that you tried to fsck an extended partition.

Alright, here's where everything is at now. it tries to boot, but fails (pic below). To me, it looks like the filesystem is totally toasted. If anyone thinks there is a way to salvage it, let me know...

Thanks

I'd be surprised if it is impossible to recover it, but I can't help you, I know nothing about Raid