From owner-freebsd-questions@FreeBSD.ORG Sun Aug 1 10:09:39 2004 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 8C08516A4CE for ; Sun, 1 Aug 2004 10:09:39 +0000 (GMT) Received: from smtp.infracaninophile.co.uk (ns0.infracaninophile.co.uk [81.2.69.218]) by mx1.FreeBSD.org (Postfix) with ESMTP id BDC7843D66 for ; Sun, 1 Aug 2004 10:09:38 +0000 (GMT) (envelope-from m.seaman@infracaninophile.co.uk) Received: from happy-idiot-talk.infracaninophile.co.uk (localhost.infracaninophile.co.uk [IPv6:::1])i71A9Hn6027882 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Sun, 1 Aug 2004 11:09:17 +0100 (BST) (envelope-from matthew@happy-idiot-talk.infracaninophile.co.uk) Received: (from matthew@localhost)id i71A9FxC027877; Sun, 1 Aug 2004 11:09:15 +0100 (BST) (envelope-from matthew) Date: Sun, 1 Aug 2004 11:09:15 +0100 From: Matthew Seaman To: "Kevin D. Kinsey, DaleCo, S.P." Message-ID: <20040801100915.GB25901@happy-idiot-talk.infracaninophile.co.uk> Mail-Followup-To: Matthew Seaman , "Kevin D. Kinsey, DaleCo, S.P." , Wojciech Puchar , freebsd-questions@freebsd.org, strick@covad.net References: <20040731222959.V41532@chylonia.3miasto.net> <20040731204517.GC75175@happy-idiot-talk.infracaninophile.co.uk> <410C62B4.80404@daleco.biz> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="mojUlQ0s9EVzWg2t" Content-Disposition: inline In-Reply-To: <410C62B4.80404@daleco.biz> User-Agent: Mutt/1.5.6i X-Greylist: Message not sent from an IPv4 address, not delayed by milter-greylist-1.5.3 (smtp.infracaninophile.co.uk [0.0.0.0]); Sun, 01 Aug 2004 11:09:17 +0100 (BST) X-Virus-Scanned: clamd / ClamAV version devel-20040705, clamav-milter version 0.74a on smtp.infracaninophile.co.uk X-Virus-Status: Clean X-Spam-Status: No, hits=-4.8 required=5.0 tests=AWL,BAYES_00 autolearn=ham version=2.63 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on happy-idiot-talk.infracaninophile.co.uk cc: strick@covad.net cc: Wojciech Puchar cc: freebsd-questions@freebsd.org Subject: Re: raw devices X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 01 Aug 2004 10:09:39 -0000 --mojUlQ0s9EVzWg2t Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Jul 31, 2004 at 10:25:40PM -0500, Kevin D. Kinsey, DaleCo, S.P. wro= te: > Matthew Seaman wrote: > >On Sat, Jul 31, 2004 at 10:30:21PM +0200, Wojciech Puchar wrote: > >>where are raw devices in FreeBSD? do they exist at all? > >Actually, all devices under FreeBSD are raw or character devices. > >Block devices on the other hand disappeared a long time ago. It's all > >to do with having an advance VM system, apparently: > > > > http://www.freebsd.org/doc/en_US.ISO8859-1/books/arch-handbook/driver= basics-block.html =20 > Hmm, now I'm a tad curious --- or confused. ceri@ just committed a > revised synopsis I hacked at for the handbook's Vinum chapter which > states, among other things: >=20 > "In addition to supporting various cards and controllers for hardware > RAID systems, the base FreeBSD system includes the Vinum Volume > Manager, a block device driver that implements virtual disk drives." >=20 > So is there conflicting data here? Might be good to figure out the > truth before the next edition handbook goes to the printer (which may be= =20 > soon...) >=20 > However, I'd be first to admit a dire lack of knowledge here... help? I think the point is not that a FreeBSD system never communicates with any device in "block mode", but that there's no exposure of that interface outside of the kernel. The original BSD distinction between character and block devices let people achieve a degree of optimization in certain circumstances by short circuiting the bufferring etc. involved in using a character device and interacting more directly with the hardware. However, that concept was first developed probably some twenty-odd years ago, and the state of the art in disk and virtual memory technology has come on a long way since then. Nowadays, short circuiting the higher levels of buffer caching just doesn't make sense. Let the VM system choose when to push blocks of data out to the disks or pseudo-disks (ie. RAID arrays, vinum devices etc), or when to read them in. It knows best. Cheers, Matthew --=20 Dr Matthew J Seaman MA, D.Phil. 26 The Paddocks Savill Way PGP: http://www.infracaninophile.co.uk/pgpkey Marlow Tel: +44 1628 476614 Bucks., SL7 1TH UK --mojUlQ0s9EVzWg2t Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (FreeBSD) iD8DBQFBDMFLiD657aJF7eIRAu5/AJ9q4DHDIiW2nO8QSKIGfWWObyvzJgCdGTHn J+RmQfvX2Lp6nJ/RTD9mY9s= =2wpk -----END PGP SIGNATURE----- --mojUlQ0s9EVzWg2t--