Re: Kernel panic from corrupt journal

[Theodore Ts'o <tytso@mit.edu>]

On Fri, Aug 31, 2012 at 09:53:07AM +0100, Brian Candler wrote:
> 
> You're quite right: yesterday I did see some I/O errors after I had mounted
> the filesystem using -o ro,noload.
> 
> So this morning I ran
> 
>   dd if=/dev/sda8 of=/dev/null bs=1024k
> 
> and it completed without a problem. And then I found I was able to mount the
> filesystem just fine!
> 
> So this is definitely a hardware problem; it's just I didn't realise I/O
> errors could cause kernel panics as well as EIO.

Well, it's not *supposed* to cause kernel panics.  If you can get a
stack trace in the future under similar circumstnaces, definitely
capture it (using a digital camera if you don't have a better way,
such as a network console or a serial console).  Even if it's not an
ext4 bug, but I'm happy to to try to route the bug report to the
appropriate kernel developer or mailing list.

> I am currently refreshing my most recent backup of this drive, and I'll
> replace it ASAP.

The drive *might* be OK at this point.  If you are willing to run a
full read/write test on the drive, and it shows no problem, it might
be worth trying to put it back in production (especially if you are
keeping regular backups); if it fails a second time, then it's
definitely time to replace it.  It's really a question of how much the
cost of a new drive is worth compared to your time and the value of
your data in case of a second failure.

Or maybe you could a buy a second 500G drive, and set up software RAID
1 using the md device.  This will give you protection if either of the
two drive fails, as well as giving you speed boost for reads.

Cheers!

						- Ted