From owner-freebsd-fs@FreeBSD.ORG Fri Dec 25 14:39:52 2009 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 8CC12106568D for ; Fri, 25 Dec 2009 14:39:52 +0000 (UTC) (envelope-from www@patpro.net) Received: from rack.patpro.net (rack.patpro.net [193.30.227.216]) by mx1.freebsd.org (Postfix) with ESMTP id 579268FC12 for ; Fri, 25 Dec 2009 14:39:52 +0000 (UTC) Received: by rack.patpro.net (Postfix, from userid 80) id 6CAE1A7; Fri, 25 Dec 2009 15:29:53 +0100 (CET) To: Barry Pederson MIME-Version: 1.0 Date: Fri, 25 Dec 2009 15:29:53 +0100 From: patpro In-Reply-To: <4B3283F2.7060804@barryp.org> References: <32CA2B73-3412-49DD-9401-4773CC73BED0@patpro.net> <4B3283F2.7060804@barryp.org> Message-ID: <3ea87f5f62bb8ba30d798d4605a64c83@localhost> X-Sender: patpro@patpro.net User-Agent: RoundCube Webmail/0.3.1 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Cc: freebsd-fs@freebsd.org Subject: Re: snapshot implementation 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, 25 Dec 2009 14:39:52 -0000 On Wed, 23 Dec 2009 14:56:18 -0600, Barry Pederson wrote: > "...there's virtually no overhead at all due to the copy-on-write > architecture. In fact, sometimes it is faster to take a snapshot rather > than free the blocks containing the old data!" > > That's certainly not the case with UFS snapshots, which can take a long > time to complete (we're talking freezing your machine's disk activity > for many minutes), and are limited to 20 total. UFS uses copy on write. But you say many minutes to complete? Don't you speak about dump(1), that uses snapshot as a basis to dump a live file system? I agree, UFS snapshot creation is not lightning-fast, but many minutes seems a lot to me, and I never experienced such a long creation time. patpro