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Date: Fri, 24 Feb 2006 11:29:57 -0500
From: "Theodore Ts'o" <tytso@mit.edu>
To: Sam Vilain <sam@vilain.net>
Cc: Xin Zhao <uszhaoxin@gmail.com>, Arjan van de Ven <arjan@infradead.org>,
       linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: question about possibility of data loss in Ext2/3 file system
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On Fri, Feb 24, 2006 at 08:46:24AM +1300, Sam Vilain wrote:
> Theodore Ts'o wrote:
> >>Also, the scheme you mentioned is just for new file creation. What
> >>will happen if I want to update an existing file? Say, I open file A,
> >>seek to offset 5000, write 4096 bytes, and then close. Do you know how
> >>ext2/3 handle this situation?
> >If you have a power failure right after the close, the data could be
> >lost.  This is true for pretty much all Unix filesystems, for
> >performance reasons.  If you care about the data hitting disk, the
> >application must use fsync().  
> 
> I always liked Sun's approach to this in Online Disk Suite - journal at 
> the block device level rather than the FS / application level. 
> Something I haven't seen from the Linux md-utils or DM.

You can do data block journalling in ext3.  But the performance impact
can be significant for some work loads.   TNSFAAFL.

						- Ted
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