From owner-freebsd-embedded@FreeBSD.ORG Tue Oct 14 17:49:39 2008 Return-Path: Delivered-To: freebsd-embedded@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id A050C1065687 for ; Tue, 14 Oct 2008 17:49:39 +0000 (UTC) (envelope-from olivier@gautherot.net) Received: from rv-out-0506.google.com (rv-out-0506.google.com [209.85.198.236]) by mx1.freebsd.org (Postfix) with ESMTP id 7F16E8FC08 for ; Tue, 14 Oct 2008 17:49:39 +0000 (UTC) (envelope-from olivier@gautherot.net) Received: by rv-out-0506.google.com with SMTP id b25so2075141rvf.43 for ; Tue, 14 Oct 2008 10:49:38 -0700 (PDT) Received: by 10.140.201.15 with SMTP id y15mr5076284rvf.145.1224005234920; Tue, 14 Oct 2008 10:27:14 -0700 (PDT) Received: by 10.141.113.11 with HTTP; Tue, 14 Oct 2008 10:27:14 -0700 (PDT) Message-ID: Date: Tue, 14 Oct 2008 15:27:14 -0200 From: "Olivier Gautherot" To: "M. Warner Losh" In-Reply-To: <20081014.110022.635731567.imp@bsdimp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <48F4C02F.1060407@syx.ca> <20081014.110022.635731567.imp@bsdimp.com> Cc: freebsd-embedded@freebsd.org Subject: Re: storage selection for embedded devices X-BeenThere: freebsd-embedded@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Dedicated and Embedded Systems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 14 Oct 2008 17:49:39 -0000 Philip, Warner, On Tue, Oct 14, 2008 at 3:00 PM, M. Warner Losh wrote: > In message: <48F4C02F.1060407@syx.ca> > Philip Mullis writes: > : I was wondering if anyone has extended experience in this area with > : embedded devices. > : > : I have a fixed embedded image which runs happily out of a 1Gig compact > : flash card. > : > : However I have some applications that I want to install to my device > : that will perform writes alot to the cf. > > I've deployed CF cards into systems for a number of years (since > 2000). They are way more reliable than spinning media in the > environments that I deploy my company's gear into. > > We have most of the CF dedicated to a read-only partition. A small > modification partition was also provided. I wonder if you're talking about the same thing (may be just me...) Philip, what frequency of writes are you talking about? I think this is key to the discussion. Are you planning enough RAM to avoid swap? Can your system count with a RAM disk and regular dump of the content to FLASH? If this is the case, a USB stick should be a safe approach. The algorithm Sandisk is referring to enhances the statistical lifespan by shuffling the cells and using spare ones when the main array wears out (trial-and-error algorithm). The typical lifespan of a cell is 100k write cycles: try to evaluate whether this is compatible with the use you plan for your device. > I've also tried to wear out a CF part by writing to the part, both > directly and through a filesystem, millions of times. I was unable to > keep a machine running long enough to cause a failure (my mistake was > doing it in a lab where people liked to unplug things). The technology has surely evolved since I last dealt with it in an industrial environment. However, I would not swear by the "millions of times" as such: Sandisk is famous for leveling the writes over the whole array. Now, if your partition is relatively empty, your device will support more cycles. In any case, using 10% of the FLASH blocks can surely lead you to the millions of cycles without problem. > : Ive read the sandisk wear leveling white paper, yet I also hear many > : people such as professional photographers swearing by the write once > : rule with cf cards. That's paranoia, especially with todays technologies. -- Olivier Gautherot olivier@gautherot.net Cel:+56 98 730 9361 www.gautherot.net http://www.linkedin.com/in/ogautherot