From owner-cvs-src@FreeBSD.ORG Mon Dec 17 16:09:40 2007 Return-Path: Delivered-To: cvs-src@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 22FB716A418; Mon, 17 Dec 2007 16:09:40 +0000 (UTC) (envelope-from des@des.no) Received: from tim.des.no (tim.des.no [194.63.250.121]) by mx1.freebsd.org (Postfix) with ESMTP id D03DC13C46E; Mon, 17 Dec 2007 16:09:39 +0000 (UTC) (envelope-from des@des.no) Received: from tim.des.no (localhost [127.0.0.1]) by spam.des.no (Postfix) with ESMTP id 9772A20A0; Mon, 17 Dec 2007 17:09:31 +0100 (CET) X-Spam-Tests: AWL X-Spam-Learn: disabled X-Spam-Score: -0.1/3.0 X-Spam-Checker-Version: SpamAssassin 3.2.3 (2007-08-08) on tim.des.no Received: from ds4.des.no (des.no [80.203.243.180]) by smtp.des.no (Postfix) with ESMTP id 868F32099; Mon, 17 Dec 2007 17:09:31 +0100 (CET) Received: by ds4.des.no (Postfix, from userid 1001) id 8368E84492; Mon, 17 Dec 2007 17:09:31 +0100 (CET) From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= To: Bruce M Simpson References: <11419.1197903331@critter.freebsd.dk> <4766951B.8090504@incunabulum.net> Date: Mon, 17 Dec 2007 17:09:31 +0100 In-Reply-To: <4766951B.8090504@incunabulum.net> (Bruce M. Simpson's message of "Mon\, 17 Dec 2007 15\:26\:19 +0000") Message-ID: <86hcihi9qc.fsf@ds4.des.no> User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/22.1 (berkeley-unix) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Cc: cvs-src@FreeBSD.org, Poul-Henning Kamp , src-committers@FreeBSD.org, "Bruce M. Simpson" , cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sbin/atacontrol atacontrol.c X-BeenThere: cvs-src@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: CVS commit messages for the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 17 Dec 2007 16:09:40 -0000 Bruce M Simpson writes: > The feedback I've seen in FreeBSD forums regarding ATA write caching > tends to back up your original assertion. It wouldn't be the first case of uninformed people reinforcing eachother's belief in incorrect information. > I wonder if vendor neutral, reproducible, scientific research has been > conducted into this issue. Scientific research? Since when does reverse engineering qualify as scientific research? > * NAND Flash embedded ATA controllers should not erase sectors > containing data unless absolutely necessary, to implement wear > levelling. No. Blocks which go from used to unused should be immediately erased. Otherwise, the device fills up with unused, unerased blocks and you end up having to erase a block every time you write to the device. Remember that cells in NAND flash can only be changed in one direction (one to zero for single-level flash) without being erased. As a result, there are very few cases (allocation bitmaps being one of them) where you can write to the same block of NAND flash multiple times without erasing it in between. > [I came across an alternative to JFFS2 awhile back whose name escapes > me, which might work for the SDIO arm stuff imp was playing with.] Specialized file systems such as JFFS and YAFFS are not very useful for flash media with built-in wear levelling, such as USB sticks or CF / SD cards. They are mostly useful for embedded devices with on-board NAND flash. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no