From owner-freebsd-fs@FreeBSD.ORG Thu Apr 27 15:23:53 2006 Return-Path: X-Original-To: freebsd-fs@freebsd.org Delivered-To: freebsd-fs@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 79CA616A401 for ; Thu, 27 Apr 2006 15:23:53 +0000 (UTC) (envelope-from scottl@samsco.org) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.FreeBSD.org (Postfix) with ESMTP id C14C243D55 for ; Thu, 27 Apr 2006 15:23:50 +0000 (GMT) (envelope-from scottl@samsco.org) Received: from [192.168.254.11] (junior.samsco.home [192.168.254.11]) (authenticated bits=0) by pooker.samsco.org (8.13.4/8.13.4) with ESMTP id k3RFNdW4000898; Thu, 27 Apr 2006 09:23:39 -0600 (MDT) (envelope-from scottl@samsco.org) Message-ID: <4450E1FD.7040008@samsco.org> Date: Thu, 27 Apr 2006 09:23:41 -0600 From: Scott Long User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.12) Gecko/20051230 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Eric Anderson References: <444FE114.7010106@mhi-tx.com> <20060426211059.GA85780@xor.obsecurity.org> <4450B3B1.8070704@centtech.com> <4450D18D.9060101@mhi-tx.com> <4450D278.5000802@centtech.com> In-Reply-To: <4450D278.5000802@centtech.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-1.4 required=3.8 tests=ALL_TRUSTED autolearn=failed version=3.1.1 X-Spam-Checker-Version: SpamAssassin 3.1.1 (2006-03-10) on pooker.samsco.org Cc: freebsd-fs@freebsd.org, Robert Subject: Re: suspend writes for external snapshot X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 27 Apr 2006 15:23:53 -0000 Eric Anderson wrote: > Robert wrote: > >> Eric Anderson wrote: >> >>> Kris Kennaway wrote: >>> >>>> On Wed, Apr 26, 2006 at 04:07:32PM -0500, Robert wrote: >>>> >>>>> Greetings, >>>>> I am trying to determine if there is a way to suspend write >>>>> activity on a FreeBSD filesystem (currently 6.0R) in order to take >>>>> a snapshot with external SAN software (Falconstor IPStor)? >>>> >>>> >>>> >>>> Use a FreeBSD snapshot and then image that? >>> >>> >>> >>> He can't do it that way because the Falconstor is a raw block device >>> and has no idea the difference between a snapshot and other >>> filesystem bits. >>> >>> >>> Robert - we have some very alpha patches in house that allow >>> suspension of UFS filesystems for things like this (also working on >>> online UFS growing). I'm not sure how close we really are to letting >>> it loose in the wild, but we will definitely be making all the >>> patches available to whomever wants it. >>> >>> >>> Eric >>> >>> >>> >> >> Sounds great thank you, I will keep an eye out for the patches. >> >> I am still unclear as to the necessity of suspending writes based on >> the following information from http://www.mckusick.com/softdep/ >> >> "By ensuring that the only inconsistencies are unclaimed blocks or >> inodes, soft updates can eliminate the need to run a filesystem check >> program after every system crash. Instead, the system is brought up >> immediately. >> >> When it is convenient, a snapshot is taken and a background task can >> be run on on that snapshot to reclaim any lost blocks and inodes. The >> use of a snapshot allows normal filesystem activity to continue >> concurrently. " >> >> Does this mean that I can take a snapshot of an in use filesystem and >> the only ill effects will be the lost blocks and inodes which can be >> reclaimed with background fsck once the snapshot is booted? > > > I believe so, yes. Someone correct me here if I am wrong. > > Ideally, yes. But for the purposes of snapshots, you want the filesystem to be flushed. Otherwise you might catch an in-progress operation like a file add/delete/truncate that would be better off finished before taking the snapshot Scott