From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Fedyk <mfedyk@matchmail.com>
Subject: Re: precise characterization of ext3 atomicity
Date: Thu, 4 Sep 2003 11:15:40 -0700
Message-ID: <20030904181540.GC13676@matchmail.com>
References: <3F574A49.7040900@namesys.com> <20030904085537.78c251b3.akpm@osdl.org> <3F576176.3010202@namesys.com> <20030904091256.1dca14a5.akpm@osdl.org> <3F57676E.7010804@namesys.com>
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To: Hans Reiser <reiser@namesys.com>
Cc: Andrew Morton <akpm@osdl.org>, reiserfs-list@namesys.com, linux-kernel@vger.kernel.org

On Thu, Sep 04, 2003 at 08:25:18PM +0400, Hans Reiser wrote:
> In data=journal and data=ordered modes ext3 also guarantees that the 
> metadata will be committed atomically with the data they point to.  However 
> ext3 does not provide user data atomicity guarantees beyond the scope of a 
> single filesystem disk block (usually 4 kilobytes).  If a single write() 
> spans two disk blocks it is possible that a crash partway through the write 
> will result in only one of those blocks appearing in the file after 
> recovery.

And how does reiser4 do this without changing the userspace apps?

Most files are written with several write() calls, so even if each call is
atomic, your entire file will not be there.

Also, ext3 could claim the same atomicity if it only updated meta-data on
write() call boundaries, instead of block boundaries.