From owner-freebsd-fs@FreeBSD.ORG Fri Nov 4 22:07:27 2005 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 1DFED16A41F for ; Fri, 4 Nov 2005 22:07:27 +0000 (GMT) (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 8DA1C43D45 for ; Fri, 4 Nov 2005 22:07:26 +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 jA4M7L5a081060; Fri, 4 Nov 2005 15:07:21 -0700 (MST) (envelope-from scottl@samsco.org) Message-ID: <436BDB99.5060907@samsco.org> Date: Fri, 04 Nov 2005 15:07:21 -0700 From: Scott Long User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.8) Gecko/20050615 X-Accept-Language: en-us, en MIME-Version: 1.0 To: user References: In-Reply-To: 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=3.1.0 X-Spam-Checker-Version: SpamAssassin 3.1.0 (2005-09-13) on pooker.samsco.org Cc: freebsd-fs@freebsd.org Subject: Re: UFS2 snapshots on large filesystems 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: Fri, 04 Nov 2005 22:07:27 -0000 user wrote: > Hello, > > Considering a PC server running FreeBSD with 4 400 GB hard drives attached > to a hardware raid controller doing raid-5. > > So this will present itself to the OS as a 1.2TB filesystem. > > Any comments on taking one or multiple snapshots of a filesystem of this > size ? > > Given current disk capacities, I would not exactly consider this 1.2TB > filesystem a "large" one ... any comments on say ... a 6-8 TB filesystem > and making one or more snapshots of it ? > > Assume they are marginally busy - perhaps a 5-10% data turnover per day... > > Thanks. > The UFS snapshot code was written at a time when disks were typically around 4-9GB in size, not 400GB in size =-) Unfortunately, the amount of time it takes to do the initial snapshot bookkeeping scales linearly with the size of the drive, and many people have reported that it takes considerable amount of time (anywhere from several minutes to several dozen minutes) on large drives/arrays like you describe. So, you should test and plan accordingly if you are interested in using them. Scott