From owner-freebsd-geom@FreeBSD.ORG Mon Jan 22 13:24:46 2007 Return-Path: X-Original-To: freebsd-geom@freebsd.org Delivered-To: freebsd-geom@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 1A05516A400 for ; Mon, 22 Jan 2007 13:24:46 +0000 (UTC) (envelope-from anderson@centtech.com) Received: from mh2.centtech.com (moat3.centtech.com [64.129.166.50]) by mx1.freebsd.org (Postfix) with ESMTP id E17B213C44C for ; Mon, 22 Jan 2007 13:24:45 +0000 (UTC) (envelope-from anderson@centtech.com) Received: from [10.177.171.220] (neutrino.centtech.com [10.177.171.220]) by mh2.centtech.com (8.13.8/8.13.8) with ESMTP id l0MDObFB025291; Mon, 22 Jan 2007 07:24:37 -0600 (CST) (envelope-from anderson@centtech.com) Message-ID: <45B4BB19.4050604@centtech.com> Date: Mon, 22 Jan 2007 07:24:41 -0600 From: Eric Anderson User-Agent: Thunderbird 1.5.0.9 (X11/20070121) MIME-Version: 1.0 To: Ivan Voras References: <20070120073117.GB60202@x12.dk> <45B456B6.6040808@centtech.com> <20070122084852.GA18648@x12.dk> <45B4B406.7060906@centtech.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: ClamAV 0.88.4/2476/Sun Jan 21 10:22:33 2007 on mh2.centtech.com X-Virus-Status: Clean X-Spam-Status: No, score=-2.1 required=8.0 tests=AWL,BAYES_00 autolearn=ham version=3.1.6 X-Spam-Checker-Version: SpamAssassin 3.1.6 (2006-10-03) on mh2.centtech.com Cc: freebsd-geom@freebsd.org Subject: Re: A beginner project X-BeenThere: freebsd-geom@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: GEOM-specific discussions and implementations List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 22 Jan 2007 13:24:46 -0000 On 01/22/07 07:12, Ivan Voras wrote: > Eric Anderson wrote: > >> Not snapshot like a photo, snapshot like 'point in time copy of storage'. >> > > I think the "current" problem with geom-based snapshots is how will they > interact with gjournal - i.e. do you snapshot the journal or not? I think it only matters if you use UFS, if you care about a consistent filesystem on the snapshot. You could probably tie a hook into geom snapshot to tell gjournal to flush the journal, take the snapshot, and then continue. A similar hook (like gjournal has) to flush the buffer down to the disk would be good to have in geom snapshot also. I actually think the hard part is keeping track of the snapshotted blocks, and keeping them in an order that doesn't completely destroy performance, while still allowing an 'instant' snapshot. UFS snapshots take a very very long time on large file systems, so a geom snapshot (to be useful) should be snappy (pun intended). Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology An undefined problem has an infinite number of solutions. ------------------------------------------------------------------------