From owner-freebsd-current@FreeBSD.ORG Sun Jan 18 20:11:56 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 4B03916A4CE for ; Sun, 18 Jan 2004 20:11:56 -0800 (PST) Received: from main.gmane.org (main.gmane.org [80.91.224.249]) by mx1.FreeBSD.org (Postfix) with ESMTP id 7659D43D45 for ; Sun, 18 Jan 2004 20:11:54 -0800 (PST) (envelope-from freebsd-current@m.gmane.org) Received: from list by main.gmane.org with local (Exim 3.35 #1 (Debian)) id 1AiQlV-0004y3-00 for ; Mon, 19 Jan 2004 05:11:53 +0100 X-Injected-Via-Gmane: http://gmane.org/ To: freebsd-current@freebsd.org Received: from sea.gmane.org ([80.91.224.252]) by main.gmane.org with esmtp (Exim 3.35 #1 (Debian)) id 1AiQlU-0004xv-00 for ; Mon, 19 Jan 2004 05:11:52 +0100 Received: from news by sea.gmane.org with local (Exim 3.35 #1 (Debian)) id 1AiQlU-0003AL-00 for ; Mon, 19 Jan 2004 05:11:52 +0100 From: Jesse Guardiani Date: Sun, 18 Jan 2004 23:11:51 -0500 Organization: WingNET Lines: 37 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7Bit X-Complaints-To: usenet@sea.gmane.org User-Agent: KNode/0.7.2 X-Mail-Copies-To: never Sender: news Subject: filesystem snapshot question X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list Reply-To: jesse@wingnet.net List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 19 Jan 2004 04:11:56 -0000 Howdy list, I've read some of the documentation written about the new filesystem snapshot feature in 5.x, and I've used it a few times on my laptop. Very very slick. However, I can't seem to find a good explanation of exactly HOW it works and what performance issues are involved. Snapshots don't seem to take up much disk space. (even though `ls -al` will report that the snapshot is as large as the slice on which it resides at the time the snapshot was created) So when a snapshot is active on a filesystem, does every disk write happen twice? Once to the real filesystem and once to the snapshot with old data? I mean, it CAN'T actually be making a copy of the filesystem. :) My disk doesn't have enough free space. Is there a way to actually figure out how much data the snapshot has allocated at any given time? Does a snapshot physically grow on the disk as changes are made to the real filesystem? Just hoping to understand things better. Thanks! -- Jesse Guardiani, Systems Administrator WingNET Internet Services, P.O. Box 2605 // Cleveland, TN 37320-2605 423-559-LINK (v) 423-559-5145 (f) http://www.wingnet.net