From owner-freebsd-fs@FreeBSD.ORG Wed Dec 23 16:41:36 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 14C9A106568F for ; Wed, 23 Dec 2009 16:41:36 +0000 (UTC) (envelope-from bfriesen@simple.dallas.tx.us) Received: from blade.simplesystems.org (blade.simplesystems.org [65.66.246.74]) by mx1.freebsd.org (Postfix) with ESMTP id D25F88FC1E for ; Wed, 23 Dec 2009 16:41:35 +0000 (UTC) Received: from freddy.simplesystems.org (freddy.simplesystems.org [65.66.246.65]) by blade.simplesystems.org (8.13.8+Sun/8.13.8) with ESMTP id nBNGfYKA006843; Wed, 23 Dec 2009 10:41:34 -0600 (CST) Date: Wed, 23 Dec 2009 10:41:34 -0600 (CST) From: Bob Friesenhahn X-X-Sender: bfriesen@freddy.simplesystems.org To: Patrick Proniewski In-Reply-To: <32CA2B73-3412-49DD-9401-4773CC73BED0@patpro.net> Message-ID: References: <32CA2B73-3412-49DD-9401-4773CC73BED0@patpro.net> User-Agent: Alpine 2.01 (GSO 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.2 (blade.simplesystems.org [65.66.246.90]); Wed, 23 Dec 2009 10:41:35 -0600 (CST) 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: Wed, 23 Dec 2009 16:41:36 -0000 On Wed, 23 Dec 2009, Patrick Proniewski wrote: > By the way, I'm also interested in ZFS: is the snapshot technology > available in ZFS the same as the one available in UFS? I don't know anything about snapshots in UFS, but snapshots in ZFS are certainly remarkably different. ZFS uses copy-on-write (COW) whenever a data block is updated and snapshot creation simply adds a new reference to existing blocks. The snapshot is made available as a (usually) hidden directory (/filesystem/.zfs/snapshot/snapname) which contains the complete filesystem content at the time the snapshot was taken. In my experience, ZFS snapshots usually take less than a second to complete. They are so efficient that some systems have snapshots scheduled to be taken every five minutes as a defense against user/application error. Bob -- Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/