From owner-freebsd-fs@FreeBSD.ORG Tue Dec 29 11:22:21 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 2C1581065698 for ; Tue, 29 Dec 2009 11:22:21 +0000 (UTC) (envelope-from patpro@patpro.net) Received: from smtp5-g21.free.fr (smtp5-g21.free.fr [212.27.42.5]) by mx1.freebsd.org (Postfix) with ESMTP id A9CD18FC08 for ; Tue, 29 Dec 2009 11:22:18 +0000 (UTC) Received: from smtp5-g21.free.fr (localhost [127.0.0.1]) by smtp5-g21.free.fr (Postfix) with ESMTP id 22F78D4802A; Tue, 29 Dec 2009 12:22:14 +0100 (CET) Received: from boleskine.patpro.net (boleskine.patpro.net [82.230.142.222]) by smtp5-g21.free.fr (Postfix) with ESMTP id B572AD480BD; Tue, 29 Dec 2009 12:22:11 +0100 (CET) Received: from [192.168.0.2] (unknown [192.168.0.2]) by boleskine.patpro.net (Postfix) with ESMTP id 18F111CCD4; Tue, 29 Dec 2009 12:22:11 +0100 (CET) Message-Id: From: Patrick Proniewski To: "Ronald Klop" In-Reply-To: Content-Type: multipart/signed; boundary=Apple-Mail-1-310690000; micalg=sha1; protocol="application/pkcs7-signature" Mime-Version: 1.0 (Apple Message framework v936) Date: Tue, 29 Dec 2009 12:22:11 +0100 References: <32CA2B73-3412-49DD-9401-4773CC73BED0@patpro.net> <4B3283F2.7060804@barryp.org> <3ea87f5f62bb8ba30d798d4605a64c83@localhost> X-Mailer: Apple Mail (2.936) X-Content-Filtered-By: Mailman/MimeDel 2.1.5 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: Tue, 29 Dec 2009 11:22:21 -0000 --Apple-Mail-1-310690000 Content-Type: text/plain; charset=ISO-8859-1; format=flowed; delsp=yes Content-Transfer-Encoding: quoted-printable On 29 d=E9c. 2009, at 11:51, Ronald Klop wrote: >>> That's certainly not the case with UFS snapshots, which can take a =20= >>> long >>> time to complete (we're talking freezing your machine's disk =20 >>> activity >>> for many minutes), and are limited to 20 total. >> >> UFS uses copy on write. But you say many minutes to complete? Don't =20= >> you >> speak about dump(1), that uses snapshot as a basis to dump a live =20 >> file >> system? >> I agree, UFS snapshot creation is not lightning-fast, but many =20 >> minutes >> seems a lot to me, and I never experienced such a long creation time. > > As far as I know UFS snapshots need to create a list of currently in =20= > use blocks. This is O(n) on the size of the FS and pauses the FS =20 > during the snapshot. On large FS's this can take a long time. > ZFS always maintains this list so it only needs to mark this list as =20= > readonly to create a snapshot. This is O(1). That's a very interesting precision. Thank you. patpro= --Apple-Mail-1-310690000--