From owner-freebsd-stable@FreeBSD.ORG Wed May 5 15:10:43 2010 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 62308106566C for ; Wed, 5 May 2010 15:10:43 +0000 (UTC) (envelope-from rizzo.unipi@gmail.com) Received: from mail-ew0-f226.google.com (mail-ew0-f226.google.com [209.85.219.226]) by mx1.freebsd.org (Postfix) with ESMTP id E98CF8FC14 for ; Wed, 5 May 2010 15:10:42 +0000 (UTC) Received: by ewy26 with SMTP id 26so1357111ewy.3 for ; Wed, 05 May 2010 08:10:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:sender:received :in-reply-to:references:date:x-google-sender-auth:message-id:subject :from:to:cc:content-type; bh=HhdC/UQWGcwUyvZReiwnvD9oDqe+YS8p4GmkITKyAWE=; b=spN/G2RDbE3ZkTdoOWCngK0HQA9zMLGSkvD6m3L2Dn/3CXKTWZUHXNf7kGPALe1rvZ Y+0er/yBZwnDYffaQaHswUYm6wyzbdjxrwNUfdGr3Qdke5K381vGTXAJiJQDQyu76SbZ YAq0giPNlmjVEMIzoGSQL5W0/Qedb7SJAgRyU= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; b=L/KpuqnFtETm2hBNZAiaDuocvtpFkQQlbgquULfUvLEv1mTqrl7fAdRTlIp9Z2vVsZ QVQFOU3w+wtZqed2hJdLYVhb9yAG/1QR8U922ExtLbYaIaCI8PiQ4vyq6SybRLo8rPNZ JAUE8+rugohzXOcCtpGhFdHTOdSQnMKe0xjAY= MIME-Version: 1.0 Received: by 10.213.42.19 with SMTP id q19mr2680968ebe.50.1273070692470; Wed, 05 May 2010 07:44:52 -0700 (PDT) Sender: rizzo.unipi@gmail.com Received: by 10.213.15.209 with HTTP; Wed, 5 May 2010 07:44:51 -0700 (PDT) In-Reply-To: <4BE17191.6040305@bsdforen.de> References: <4BE17191.6040305@bsdforen.de> Date: Wed, 5 May 2010 16:44:51 +0200 X-Google-Sender-Auth: f3pr7Rw29kKHMYXX_DuwnLVD06s Message-ID: From: Luigi Rizzo To: Dominic Fandrey Content-Type: text/plain; charset=ISO-8859-1 Cc: freebsd-stable@freebsd.org Subject: Re: geom_sched influence on SU consistency X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 05 May 2010 15:10:43 -0000 On Wed, May 5, 2010 at 3:24 PM, Dominic Fandrey wrote: > I'm wondering how geom_sched influences soft-update consistency. > > To my understanding it's very important to SU, that the file system > controls writing sequences. Because geom_sched is transparent, > i.e. UFS does not know about access scheduling, I'm afraid that > the use of geom_sched would endanger my file system consistency > in case of a crash. > > Can anyone put my fears to rest or confirm them? geom_sched is no different from the standard (elevator) disk scheduler or tagged queueing -- these system may already serve queued requests out of order. if a client wants to enforce a specific ordering of requests it can easily do so by waiting the completion of a previous request before issuing a new one.