linux-ext4 - Re: fsync() errors is unsafe and risks data loss

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Message-ID: <20180412101926.lhhu6enlgemsotwo@rh_laptop>
Date:   Thu, 12 Apr 2018 12:19:26 +0200
From:   Lukas Czerner <lczerner@...hat.com>
To:     Andres Freund <andres@...razel.de>
Cc:     Dave Chinner <david@...morbit.com>,
        Andreas Dilger <adilger@...ger.ca>,
        20180410184356.GD3563@...nk.org,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Jeff Layton <jlayton@...hat.com>,
        "Joshua D. Drake" <jd@...mandprompt.com>
Subject: Re: fsync() errors is unsafe and risks data loss

On Wed, Apr 11, 2018 at 07:32:21PM -0700, Andres Freund wrote:

> And there's cases where that just doesn't help at all. Being able to
> untar a database from backup / archive / timetravel / whatnot, and then
> fsyncing the directory tree to make sure it's actually safe, is really
> not an insane idea.  Or even just cp -r ing it, and then starting up a
> copy of the database.  What you're saying is that none of that is doable
> in a safe way, unless you use special-case DIO using tooling for the
> whole operation (or at least tools that fsync carefully without ever
> closing a fd, which certainly isn't the case for cp et al).

Does not seem like a problem to me, just checksum the thing if you
really need to be extra safe. You should probably be doing it anyway if
you backup / archive / timetravel / whatnot.

-Lukas