Invalid superblock after e2fsck

[Eric Sandeen]

Albert Sellarès wrote:
> Hi all,
> 
> I'm trying to fix a 7.5Tb ext3 filesystem using e2fsck on a x86_64
> machine with plenty of memory ram. The filesystem is corrupted, but I
> can mount it.
> 
> Before starting the filesystem check, I did a LVM snapshot to be able to
> start it again from the same point in case of error.
> 
> After 12 hours checking the filesystem, I got this error message:
> 
> Pass 1: Memory used: 268k/18014398508105072k (59k/210k), time:
> 65673.66/1550.92/1371.06
> Pass 1: I/O read: 253456MB, write: 23885MB, rate: 4.22MB/s
> Restarting e2fsck from the beginning...
> e2fsck: Superblock invalid, trying backup blocks...
> e2fsck: Bad magic number in super-block while trying to
> open /dev/storage/cabina_snapshot
> 
> Once I saw this message, my first thought was that e2fsck didn't manage
> to fix the filesystem and it corrupted the superblock. To be sure I
> dumped the entire block and compared it against the original superblock.
> Doing that I realized that the entire superblock only contained zeros.
> 
> Any ideas of what can I do? 

What is the blocksize of your filesystem?  RHEL4 should be safe for
2^31 blocks, which -should- get you to 8T at 4k blocks.

dumpe2fs -h info would show us (long as you have an intact superblock
somewehre...)

But if you were beyond 2^31 blocks I imagine you'd have hit troubles early on.

-Eric