Date: Tue, 14 Jun 2011 15:36:30 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: markgross@thegnar.org
Cc: Pavel Machek <pavel@ucw.cz>, "Rafael J. Wysocki" <rjw@sisk.pl>,
        Raffaele Recalcati <lamiaposta71@gmail.com>,
        linux-pm@lists.linux-foundation.org,
        davinci-linux-open-source@linux.davincidsp.com,
        linux-kernel@vger.kernel.org
Subject: Re: [linux-pm] pm loss development
Message-ID: <20110614153630.023eeeef@lxorguk.ukuu.org.uk>
In-Reply-To: <20110614140642.GA14509@gvim.org>
References: <1305220265-9020-1-git-send-email-lamiaposta71@gmail.com>
	<201105180107.58078.rjw@sisk.pl>
	<20110518031203.GA3640@gvim.org>
	<201105182143.13237.rjw@sisk.pl>
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	<20110614140642.GA14509@gvim.org>
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> I know nothing about journalling file systems or how well they limit the
> critical sections of time where the file system is exposed to corruption
> from sudden power failure.  Its an interesting question though.

A properly written journalling file system has no critical sections. The
only things it relies upon are

- store ordering in the drive working properly
- a single disk block write being atomic

the former is well specified even for ATA devices, the latter is a pretty
safe property of rotating media, although in theory you have a finite
chance of getting a bad sector.

For flash it's a lot lot more complicated but for a flash device claiming
to be ATA compliant you ought to get ATA behaviour.

All that said there is still (as ever) a tiny chance your system may
malfunction. It's all down to probabilities and if your laptop explodes
you need a backup (trust me, I've tested this case).

Alan

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