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Date: Wed, 26 Jan 2005 12:25:41 -0500
From: David Schultz <das@FreeBSD.ORG>
To: Arne WXrner <arne_woerner@yahoo.com>
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cc: freebsd-fs@FreeBSD.ORG
Subject: Re: ufs+softupdates / consistency
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On Wed, Jan 26, 2005, Arne WXrner wrote:
> Hi!
> 
> On
>   http://e2fsprogs.sourceforge.net/ext2intro.html
> I found the strings
>   "BSD-like synchronous updates"
>   "it can cause corruption in the user data" .
> 
> On
>   http://www.mckusick.com/softdep/
> I did not find such a statement.
> 
> Are soft updates safe for user data? I do not really understand,
> what the first www page means... Maybe they mean, that the new
> file size (that would be meta data, I think) is written before the
> user data, so that the file contains undetermined data in its
> tail.

The ext2fs paper you refer to was published at about the same time
as Ganger and Patt's Soft Updates paper, so I think it's safe to
say that the authors of the former didn't know about Soft Updates.
The comments you refer to that seem to imply that synchronous
updates are unsafe and asynchronous updates are safer are wrong in
general (synchronous updates are safer), but the authors may be
referring to bugs in the ext2fs implementation at that time.
Soft Updates, in contrast, provides asynchronous updates, issued
in an order that makes them safe.