Re: FS hang when creating snapshots on a UFS SU+J setup

> Date: Mon, 9 Jan 2012 18:30:51 +0100
> From: Yamagi Burmeister <lists_at_yamagi.org>
> To: jeff_at_freebsd.org, mckusick_at_freebsd.org
> Cc: freebsd-current_at_freebsd.org, bryce_at_bryce.net
> Subject: Re: FS hang when creating snapshots on a UFS SU+J setup
> 
> Hello,
> 
> I'm sorry to bother you, but you may not be aware of this thread and
> this problem. We are several people experiencing deadlocks, kernel
> panics and other problems when creating sanpshots on file systems
> with SU+J. It would be nice to get some feedback, e.g. how can we
> help debugging and / or fixing this problem.
> 
> Thank you,
> Yamagi

First step in debugging is to find out if the problem is SU+J
specific. To find out, turn off SU+J but leave SU. This change
is done by running:

	umount <filesystem>
	tunefs -j disable <filesystem>
	mount <filesystem>
	cd <filesystem>
	rm .sujournal

You may want to run `fsck -f' on the filesystem while you have
it unmounted just to be sure that it is clean. Then run your
snapshot request to see if it still fails. If it works, then
we have narrowed the problem down to something related to SU+J.
If it fails then we have a broader issue to deal with.

If you wish to go back to using SU+J after the test, you can
reenable SU+J by running:

	umount <filesystem>
	tunefs -j enable <filesystem>
	mount <filesystem>

When responding to me, it is best to use my <mckusick_at_mckusick.com>
email as I tend to read it more regularly.

	Kirk McKusick