linux-kernel - Re: Linux 2.6.29

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Date:	Mon, 30 Mar 2009 09:13:14 +0200
From:	"Andreas T.Auer" <andreas.t.auer_lkml_73537@...us.ath.cx>
To:	Theodore Tso <tytso@....edu>, Mark Lord <lkml@....ca>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Jeff Garzik <jeff@...zik.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rees <drees76@...il.com>, Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29


On 30.03.2009 02:39 Theodore Tso wrote:
> All I can do is apologize to all other filesystem developers profusely
> for ext3's data=ordered semantics; at this point, I very much regret
> that we made data=ordered the default for ext3.  But the application
> writers vastly outnumber us, and realistically we're not going to be
> able to easily roll back eight years of application writers being
> trained that fsync() is not necessary, and actually is detrimental for
> ext3.
>
>   
It seems you still didn't get the point. ext3 data=ordered is not the
problem. The problem is that the average developer doesn't expect the fs
to _re-order_ stuff. This is how most common fs did work long before
ext3 has been introduced. They just know that there is a caching and
they might lose recent data, but they expect the fs on disk to be a
snapshot of the fs in memory at some time before the crash (except when
crashing while writing). But the re-ordering brings it to the state that
never has been in memory. data=ordered is just reflecting this thinking.
With data=writeback as the default the users would have lost data and
would have simply chosen a different fs instead of twisting the params.
Or the distros would have made data=ordered the default to prevent
beeing blamed for the data loss.

And still I don't know any reason, why it makes sense to write the
metadata to non-existing data immediately instead of delaying that, too.

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