linux-kernel - Re: Linux 2.6.29

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Date:	Wed, 25 Mar 2009 11:34:53 +0200
From:	Benny Halevy <bhalevy@...asas.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>, Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	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 Mar. 24, 2009, 21:55 +0200, Jeff Garzik <jeff@...zik.org> wrote:
> Linus Torvalds wrote:
>> But I really don't understand filesystem people who think that "fsck" is 
>> the important part, regardless of whether the data is valid or not. That's 
>> just stupid and _obviously_ bogus.
> 
> I think I can understand that point of view, at least:
> 
> More customers complain about hours-long fsck times than they do about 
> silent data corruption of non-fsync'd files.
> 
> 
>> The point is, if you write your metadata earlier (say, every 5 sec) and 
>> the real data later (say, every 30 sec), you're actually MORE LIKELY to 
>> see corrupt files than if you try to write them together.
>>
>> And if you write your data _first_, you're never going to see corruption 
>> at all.
> 
> Amen.
> 
> And, personal filesystem pet peeve:  please encourage proper FLUSH CACHE 
> use to give users the data guarantees they deserve.  Linux's sync(2) and 
> fsync(2) (and fdatasync, etc.) should poke the block layer to guarantee 
> a media write.

I completely agree.  This also applies to nfsd_sync, by the way.
What's the right place to implement that?
How about sync_blockdev?

Benny

> 
> 	Jeff
> 
> 
> P.S.  Overall, I am thrilled that this ext3/ext4 transition and 
> associated slashdotting has spurred debate over filesystem data 
> guarantees.  This is the kind of discussion that has needed to happen 
> for years, IMO.
> 
> 
> 
> --
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-- 
Benny Halevy
Software Architect
Panasas, Inc.
bhalevy@...asas.com
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