Message-ID: <3AB67134.762CFF32@didntduck.org>
Date: Mon, 19 Mar 2001 15:51:00 -0500
From: Brian Gerst <bgerst@didntduck.org>
MIME-Version: 1.0
To: root@chaos.analogic.com
CC: Otto Wyss <otto.wyss@bluewin.ch>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Linux should better cope with power failure
In-Reply-To: <Pine.LNX.3.95.1010319150027.9639A-100000@chaos.analogic.com>
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Sender: linux-kernel-owner@vger.kernel.org

"Richard B. Johnson" wrote:
> 
> On Mon, 19 Mar 2001, Otto Wyss wrote:
> 
> > Lately I had an USB failure, leaving me without any access to my system
> > since I only use an USB-keyboard/-mouse. All I could do in that
> > situation was switching power off and on after a few minutes of
> > inactivity. From the impression I got during the following startup, I
> > assume Linux (2.4.2, EXT2-filesystem) is not very suited to any power
> > failiure or manually switching it off. Not even if there wasn't any
> > activity going on.
> >
> > Shouldn't a good system allways try to be on the save side? Shouldn't
> > Linux try to be more fail save? There is currently much work done in
> > getting high performance during high activity but it seems there is no
> > work done at all in getting a save system during low/no activity. I
> > think this is a major drawback and should be addressed as fast as
> > possible. Bringing a system to save state should allway have a high priority.
> >
> > How could this be accomplished:
> > 1. Flush any dirty cache pages as soon as possible. There may not be any
> > dirty cache after a certain amount of idle time.
> > 2. Keep open files in a state where it doesn't matter if they where
> > improperly closed (if possible).
> > 3. Swap may not contain anything which can't be discarded. Otherwise
> > swap has to be treated as ordinary disk space.
> >
> > These actions are not filesystem dependant. It might be that certain
> > filesystem cope better with power failiure than others but still it's
> > much better not to have errors instead to fix them.
> >
> > Don't we tell children never go close to any abyss or doesn't have
> > alpinist a saying "never go to the limits"? So why is this simple rule
> > always broken with computers?
> >
> 
> Unix and other such variants have what's called a Virtual File System
> (VFS).  The idea behind this is to keep as much recently-used file stuff
> in memory so that the system can be as fast as if you used a RAM disk
> instead of real physical (slow) hard disks. If you can't cope with this,
> use DOS. 

At the very least the disk should be consistent with memory.  If the
dirty pages aren't written back to the disk (but not necessarily removed
from memory) after a reasonable idle period, then there is room for
improvement.

--

				Brian Gerst
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