Re: SU+J systems do not fsck themselves

On Tue, Dec 27, 2011 at 1:53 PM, David Thiel
<lx_at_redundancy.redundancy.org> wrote:
> I've had multiple machines now (9.0-RC3, amd64, i386 and earlier
> 9-CURRENT on ppc) running SU+J that have had unexplained panics and
> crashes start happening relating to disk I/O. When I end up running a
> full fsck, it keeps turning out that the disk is dirty and corrupted,
> but no mechanism is in place with SU+J to detect and fix this. A bgfsck
> never happens, but a manual fsck in single-user does indeed fix the
> crashing and weird behavior. Others have tested their SU+J volumes and
> found them to have errors as well. This makes me super nervous.
>
> Basically, the way SU+J seems to operate is this:
>
> http://redundancy.redundancy.org/fscklog2
>
> "Oh hey, I see you shut down uncleanly, let's check everything looks
> good, off you go, whee"
>
> Until I actually go and fsck, when I get:
>
> http://redundancy.redundancy.org/fscklog1
>
> So, I understand that journalling doesn't replace the need for a
> potential fsck (though I never had this problem with gjournal), but
> without a way for the system to detect that a fsck is necessary, this
> seems pretty much a guaranteed recipe for data corruption, and seems to
> offer little to no benefit over plain SU+fsck, or even just mounting
> async.
>
> So: is everyone else seeing this? Am I misunderstanding how SU+J should
> be used? How should the error resolution process really happen?

I'm not sure if your experiments are right here, the second log shows
you're running it read-only, which is likely caused by running it on
live file system.  What I would suggest to do is:

 - Reset the system while it's running;
 - Boot into single user mode;
 - 'dd' the disk image to an image;
 - Boot the system normally and:
    - use mdconfig -a -t vnode -f on copy of the image
    - use journalled fsck;
    - use normal fsck to check if the journalled fsck did the right thing.

This would rule out possible after-mount introduced changes, etc.  I
personally did not hit problems a few months ago but I didn't re-test
recently.

Cheers,
-- 
Xin LI <delphij_at_delphij.net> https://www.delphij.net/
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