linux-kernel - Re: writing file to disk: not as easy as it looks

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Date:	Tue, 02 Dec 2008 11:22:58 -0600
From:	"Chris Friesen" <cfriesen@...tel.com>
To:	Theodore Tso <tytso@....edu>
CC:	Pavel Machek <pavel@...e.cz>, mikulas@...ax.karlin.mff.cuni.cz,
	clock@...ey.karlin.mff.cuni.cz,
	kernel list <linux-kernel@...r.kernel.org>, aviro@...hat.com
Subject: Re: writing file to disk: not as easy as it looks

Theodore Tso wrote:

> Even for ext3/ext4 which is doing physical journalling, it's still the
> case that the journal commits first, and it's only later when the
> write happens that we write out the change.  If the disk fails some of
> the writes, it's possible to lose data, especially if the two blocks
> involved in the node split are far apart, and the write to the
> existing old btree block fails.

Yikes.  I was under the impression that once the journal hit the platter 
then the data were safe (barring media corruption).

It seems like the more I learn about filesystems, the more failure modes 
there are and the fewer guarantees can be made.  It's amazing that 
things work as well as they do...

Chris
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