Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932628AbWCAAFe (ORCPT ); Tue, 28 Feb 2006 19:05:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932727AbWCAAFd (ORCPT ); Tue, 28 Feb 2006 19:05:33 -0500 Received: from dilbert.robsims.com ([209.120.158.98]:49672 "EHLO mail.robsims.com") by vger.kernel.org with ESMTP id S932628AbWCAAFd (ORCPT ); Tue, 28 Feb 2006 19:05:33 -0500 Date: Tue, 28 Feb 2006 17:05:28 -0700 From: Rob Sims To: Phillip Susi Cc: Jan Engelhardt , Sam Vilain , Luke-Jr , Jesper Juhl , Bernhard Rosenkraenzer , linux-kernel@vger.kernel.org Subject: Re: [slightly OT] dvdrecord 0.3.1 -- and yes, dev=/dev/cdrom works ;) Message-ID: <20060301000528.GD3503@robsims.com> References: <200602250042.51677.bero@arklinux.org> <200602261330.15709.luke@dashjr.org> <9a8748490602260529h3a2890bhce4112feefb7cb1f@mail.gmail.com> <200602261339.13821.luke@dashjr.org> <44049D5A.1010806@cfl.rr.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="wULyF7TL5taEdwHz" Content-Disposition: inline In-Reply-To: <44049D5A.1010806@cfl.rr.com> User-Agent: Mutt/1.5.11+cvs20060126 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3416 Lines: 85 --wULyF7TL5taEdwHz Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Feb 28, 2006 at 01:58:34PM -0500, Phillip Susi wrote: > Jan Engelhardt wrote: > >Yes. A 650 MB *CD*-RW (DVD-RW too?) formatted in packet mode only has li= ke > >500-something megabytes to allow for the sort of seeks required. > >On DVD+RW, you get the full 4.3 GB (4.7 gB) AFAICS. =20 > DVD-RAM physically is formatted like a hard disk. It is broken up into= =20 > zones that hold different numbers of sectors which are individually and= =20 > randomly read/writable. CD/DVD+-RW media is organized as a single long= =20 > groove that consists of an unbroken series of large blocks composed of=20 > small blocks with user and control data interleaved and error corrected.= =20 > It is for this reason that historically it could only be recorded from= =20 > start to finish in one pass. While DVD-RAM has per-sector embossing of headers, the ECC size is still 16 sectors, so writing any one sector requires a read-modify-write pass. =20 > There are two modern techniques to allow pseudo random write access for= =20 > all forms of CD/DVD +/- RW media. These are packet mode, and mount=20 > rainier mode. MRW mode formats the disk into 32 KB blocks made up of=20 > 2048 byte sectors which are individually writable as far as the OS=20 > knows, because an MRW compliant drive is required to internally handle=20 > any required read/modify/write cycles to update the 32 KB blocks. MRW=20 > mode also reserves some of the disk for sector sparing which the drive=20 > firmware also handles. MRW mode is typically used on dvd+rw media.=20 > IIRC, this format typically "wastes" about 10% of the capacity of the=20 > medium. DVD+RW and theoretically DVD-RW support writing of 32K chunks randomly on the disk. DVD+RW has a tight tolerance on positioning (+/-16 bits) and DVD-RW about 150 bytes. Both rely on ECC to correct those bits, though DVD+RW obviously eats less of the ECC budget. Neither format uses a special packet format. The drives themselves are supposed to do read-modify-write as required. > The other technique is packet mode. Packet mode formats the media into= =20 > packets of sectors and each packet can be randomly rewritten. The=20 > current default size is only 32 sectors per packet. Each packet has 7=20 > sectors of linking loss so around 18% of the disk space is wasted. I=20 > recently submitted a patch to pktcdvd and have some patches to the=20 > udftools package to support larger packet sizes. A packet size of 128=20 > sectors reduces the waste to only 5.2%. =20 Fixed packet writing is only a CD attribute. Using 128 sector packets will likely break UDF interchangeability, and likely even some drive firmware. --=20 Rob --wULyF7TL5taEdwHz Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2 (GNU/Linux) iD8DBQFEBOVInvKppSZW8osRAgBjAJ4/ib3d91Ko4/WRhscdxtu8u+SHHgCfQley FUVTKn2c4KRnJxkU4+7dsnQ= =FamV -----END PGP SIGNATURE----- --wULyF7TL5taEdwHz-- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/