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Date:      Tue, 6 Feb 2001 12:33:00 -0800
From:      Alfred Perlstein <bright@wintelcom.net>
To:        Andre Oppermann <oppermann@monzoon.net>
Cc:        Rik van Riel <riel@conectiva.com.br>, Matt Dillon <dillon@earth.backplane.com>, Mike Silbersack <silby@silby.com>, Poul-Henning Kamp <phk@critter.freebsd.dk>, Charles Randall <crandall@matchlogic.com>, Dan Phoenix <dphoenix@bravenet.com>, Jos Backus <josb@cncdsl.com>, freebsd-hackers@FreeBSD.ORG
Subject:   Re: soft updates and qmail (RE: qmail IO problems)
Message-ID:  <20010206123259.U26076@fw.wintelcom.net>
In-Reply-To: <3A805E94.8FF4F103@monzoon.net>; from oppermann@monzoon.net on Tue, Feb 06, 2001 at 09:29:08PM %2B0100
References:  <Pine.LNX.4.21.0102061822240.1535-100000@duckman.distro.conectiva> <3A805E94.8FF4F103@monzoon.net>

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* Andre Oppermann <oppermann@monzoon.net> [010206 12:30] wrote:
> Rik van Riel wrote:
> > 
> > On Tue, 6 Feb 2001, Andre Oppermann wrote:
> > 
> > > But please answer me one question: Is the link() call atomically
> > > in FFS/UFS w or w/o softupdates? Meaning when the call returns
> > > the meta- data is written to stable storage like with fsync()?
> > 
> > Since when does `atomic' equal `synchronous' ?
> 
> Because otherwise it would not be atomically, would it?

Softupdates does it atomically but not synchronously. :)

Basically, the in-memory view of the filesystem != the on-disk
version.

The update happens atomically with respect to locking in memory,
so running processes never see a non-atomic snapshot of the directory,
but if a crash occurs the disk may be several steps behind the
memory at the time of the crash.

-- 
-Alfred Perlstein - [bright@wintelcom.net|alfred@freebsd.org]
"I have the heart of a child; I keep it in a jar on my desk."


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