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Date:      Mon, 14 Oct 2013 14:51:55 -0400 (EDT)
From:      Daniel Feenberg <feenberg@nber.org>
To:        Bruce Cran <bruce@cran.org.uk>
Cc:        David Demelier <demelier.david@gmail.com>, Adam Vande More <amvandemore@gmail.com>, Brad Mettee <bmettee@pchotshots.com>, FreeBSD Questions <freebsd-questions@freebsd.org>, CeDeROM <cederom@tlen.pl>
Subject:   Re: SU+J Lost files after a power failure
Message-ID:  <alpine.LRH.2.03.1310141447520.16969@nber.org>
In-Reply-To: <525C2FBC.4080808@cran.org.uk>
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>

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On Mon, 14 Oct 2013, Bruce Cran wrote:

> On 10/14/2013 6:16 PM, CeDeROM wrote:
>> Isn't there Journal to prevent and reverse such damage?
>
> Unlike other journaling filesystems, UFS+J only protects the metadata, not 
> the data itself - i.e. I think it ensures you won't have to run a manual 
> fsck, but just like plain old UFS files may be truncated as the journal is 
> replayed.

This discussion skirts the critical issue - are files that are not open 
for writing endangered? No description of the uses of journaling can be 
considered informative if it doesn't address that explicitly. As a naive 
user I have always assumed that once closed, a file was invulnerable to 
improper shutdowns, but this discussion shakes that belief.

I expect the answer may be different for SSD and spinning disks.

dan feenberg



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