To: "Alexander E. Patrakov" <patrakov@gmail.com>
Cc: Pavel Machek <pavel@suse.cz>, kernel list <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, tytso@mit.edu, mtk.manpages@gmail.com,
       rdunlap@xenotime.net, linux-doc@vger.kernel.org,
       Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: document ext3 requirements
In-Reply-To: Your message of "Sun, 04 Jan 2009 18:35:41 +0500."
             <4960BB2D.3060000@gmail.com>
From: Valdis.Kletnieks@vt.edu
References: <20090103123813.GA1512@ucw.cz>
            <4960BB2D.3060000@gmail.com>
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Date: Sun, 04 Jan 2009 08:53:15 -0500
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On Sun, 04 Jan 2009 18:35:41 +0500, "Alexander E. Patrakov" said:

> Ext3 means either hardware that supports barriers (not sure how to 
> check, and anyway I have to use encryption on the work laptop due to the 
> corporate policy) or disabling write cache (but, as Alan Cox said, this 
> shortens the lifespan of the disk).

False dichotomy.  This isn't an "either/or", as there's a *third* case:

"understand the issues and risks involved if you have a write cache and
no barrier support, and learn to deal with it".

As you point out, if it's a laptop with a battery, the risk may be *very* low.
Let's say there's a 1 in 10,000 chance that you'll trash a file system and
need to restore from backups.

That may be totally acceptable if you've already estimated a 1 in 500 chance
of the whole damned laptop going walkies while you're not looking, and then
you *still* need to be able to restore from backups onto a replacement machine.

Yes, for some systems, the whole barriers/write cache thing is in fact very
important.  But for others, data loss due to spilled coffee is a bigger worry...

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