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Date:      Tue, 8 Dec 2009 13:32:09 +0100 (CET)
From:      Konrad Heuer <kheuer2@gwdg.de>
To:        cronfy <cronfy@sprinthost.ru>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: FreeBSD is too filesystem errors sensitive
Message-ID:  <20091208132720.G67127@gwdu60.gwdg.de>
In-Reply-To: <20091208113023.GA1828@owl.midgard.homeip.net>
References:  <4B1DF953.4050504@sprinthost.ru> <hfl7v5$f9j$1@ger.gmane.org> <4B1E2D40.9060900@sprinthost.ru> <20091208114509.B67127@gwdu60.gwdg.de> <4B1E33CF.1070309@sprinthost.ru> <20091208113023.GA1828@owl.midgard.homeip.net>

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On Tue, 8 Dec 2009, Erik Trulsson wrote:

> On Tue, Dec 08, 2009 at 02:09:03PM +0300, cronfy wrote:
>>
>>>>>>  panics like 'freeing free block' or 'ffs_valloc: dup alloc'
>>>>
>>>> Is there a way to say "Dear kernel, don't panic, I'am holding your
>>>> hand, keep working please-please-please?" If so, can it lead to
>>>> complete filesystem corruption indeed or it is not so serious?
>>>
>>> Afaik you can't do this. And you shouldn't do if it'd be possible. The
>>> file system errors you mention above should not happen under any
>>> normal circumstances. They may happen after a crash caused by other
>>> reasons but should get repaired by fsck. The kernel cannot continue
>>> with such errors because the whole file system metadata cannot be
>>> trusted anymore until repaired.
>>>
>> Thanks.
>>
>> What I can definitely state is that after reboot nothing will get any
>> better. I will have same filesystem with same errors + new errors that
>> appeared because soft-updates were not synced, and I will have fsck
>> running in background. I'd prefer to just start fsck in background,
>> skipping that annoying reboot phase ;-) Am I willing strange?
>
> Background fsck can only handle a few, very specific, filsystem problems.
> (Basically situations where blocks are marked as being in use, even though
> they are not really used by anything.  Softupdates is supposed to guarantee
> that those are the only types of filesystem errors that can occur, but in
> reality that guarantee does not always hold.)
>
> If you have other instances of filesystem corruption (which includes
> everything which can trigger a kernel panic) you need to use a foreground
> fsck to fix it.

That's true. You should go down to single user mode by entering "shutdown 
now", unmount your filesystems ("umount -a -t ufs") and check your 
filesystem by "fsck -y". Please read "man fsck" before since implicitly 
answering all questions with yes by "-y" may cause loss of data !!!

(To tell the truth: You probably have to do so anyway.)

> Personally I would recommend not using background fsck at all unless you
> know exactly what you are doing and why.

Best regards

Konrad Heuer
GWDG, Am Fassberg, 37077 Goettingen, Germany, kheuer2@gwdg.de




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