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Date:      Mon, 14 Oct 2013 15:21:17 -0700
From:      Charles Swiger <cswiger@mac.com>
To:        RW <rwmaillists@googlemail.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: SU+J Lost files after a power failure
Message-ID:  <89DF80F4-E426-4457-BDBF-958B1CBDB52F@mac.com>
In-Reply-To: <20131014204125.6cc4a31e@gumby.homeunix.com>
References:  <525A6831.5070402@gmail.com> <l3gc7e$c91$1@ger.gmane.org> <20131014133953.58f74659@gumby.homeunix.com> <525C1D1C.9050708@gmail.com> <CA+tpaK2Pr2po2cQ1yanQK9+wLp77SYqYHjxiXaU5FfXwHrkGow@mail.gmail.com> <CAFYkXjn-1wTJcQ4a_fyXCvwh9ukt3+djM2qsMeaH1HhVJNvhiA@mail.gmail.com> <525C2554.7080203@pchotshots.com> <CAFYkXjm8y0Br31_pqRZc0sNFbqCNtKHhjeQuiLXkGT2zxSu0GA@mail.gmail.com> <525C2FBC.4080808@cran.org.uk> <CAFYkXj==tiKSAJh3kkCnonsqAaDg_sHYYEUnfLKWLaR-GD-Nzw@mail.gmail.com> <F2D0FD23-884F-48D4-865B-CE793E2B4F39@mac.com> <20131014204125.6cc4a31e@gumby.homeunix.com>

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On Oct 14, 2013, at 12:41 PM, RW <rwmaillists@googlemail.com> wrote:
> On Mon, 14 Oct 2013 11:48:18 -0700 Charles Swiger wrote:
>> Yes.  Without journalling, you'd normally perform the full
>> timeconsuming fsck in the foreground.
> 
> Journalling removes the need for the background fsck which only recovers
> lost space. 

That and inode link changes (ie, adding or removing files from a directory).

>> With journalling, it should be able to do a journal replay to restore
>> the filesystem to an OK state,
> 
> My understanding is that the journal does nothing to restore the
> filesystem other than keep track of orphaned memory. In all other
> respect it's the job of soft-updates to keep the filesystem in an OK
> state.

Yes, SU is supposed to reorder filesystem operations to provide some level
of "ACID" transaction semantics-- and the journal helps that by avoiding
the need for bgfsck.

> When it doesn't you need a foreground check.
> 
>> but sometimes that doesn't restore consistency, in which case it
>> usually fires off a background fsck rather than the foreground fsck.
> 
> I think if the journal fails, you would really need to run at least a
> foreground preen, maybe a full fsck. 

Yes.

Regards,
-- 
-Chuck




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