From owner-freebsd-current  Tue Mar  3 14:22:47 1998
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Received: (from majordom@localhost)
          by hub.freebsd.org (8.8.8/8.8.8) id OAA25994
          for freebsd-current-outgoing; Tue, 3 Mar 1998 14:22:47 -0800 (PST)
          (envelope-from owner-freebsd-current@FreeBSD.ORG)
Received: from alpo.whistle.com (alpo.whistle.com [207.76.204.38])
          by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id OAA25960
          for <freebsd-current@FreeBSD.ORG>; Tue, 3 Mar 1998 14:22:34 -0800 (PST)
          (envelope-from julian@whistle.com)
Received: (from daemon@localhost)
	by alpo.whistle.com (8.8.5/8.8.5) id OAA19444;
	Tue, 3 Mar 1998 14:11:08 -0800 (PST)
Received: from UNKNOWN(), claiming to be "current1.whistle.com"
 via SMTP by alpo.whistle.com, id smtpd019441; Tue Mar  3 14:11:02 1998
Message-ID: <34FC7EFC.237C228A@whistle.com>
Date: Tue, 03 Mar 1998 14:06:52 -0800
From: Julian Elischer <julian@whistle.com>
Organization: Whistle Communications
X-Mailer: Mozilla 3.0Gold (X11; I; FreeBSD 2.2.5-RELEASE i386)
MIME-Version: 1.0
To: "Alok K. Dhir" <adhir@worldbank.org>
CC: roberto@keltia.freenix.fr, freebsd-current@FreeBSD.ORG
Subject: Re: Panic with CURRENT & softupdates-240298
References: <Pine.NEB.3.96.980303164538.6994B-100000@shadow.worldbank.org>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: owner-freebsd-current@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

Alok K. Dhir wrote:
> 
> Mind explaining what soft-updates does?
> 


Soft Updates is a method of keeping track of teh dependencies
within the metadata of a filesystem, so that you can ensure 
that at every stage, the on-disk image is consistent. It 
includes such techniques as temporarily backing out certain 
changes during disk writes, and queuing up a lot 
of extra information. 

This seems a lot of work, however the gain is that:
1/ after a crash fsck is not really required.
(except to recover blocks marked in use but really freed in 
the last few seconds of running before the crash) 
2/ The writes are ALL (unles you do a fsync()) done async,
3/ The dependencies automatically notice things like:
   "I'm about to write a file but it's already been deleted"
   and cancels the operation.
4/ metadata operations such as deletion are grouped up and
done in bulk which is WAY faster.

(that's just a quick start)

julian

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message