From owner-freebsd-embedded@FreeBSD.ORG Tue Oct 14 17:02:05 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 61642106568F for ; Tue, 14 Oct 2008 17:02:05 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from harmony.bsdimp.com (bsdimp.com [199.45.160.85]) by mx1.freebsd.org (Postfix) with ESMTP id 0269C8FC26 for ; Tue, 14 Oct 2008 17:02:04 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from localhost (localhost [127.0.0.1]) by harmony.bsdimp.com (8.14.2/8.14.1) with ESMTP id m9EGxML2066173; Tue, 14 Oct 2008 10:59:22 -0600 (MDT) (envelope-from imp@bsdimp.com) Date: Tue, 14 Oct 2008 11:00:22 -0600 (MDT) Message-Id: <20081014.110022.635731567.imp@bsdimp.com> To: philip.mullis@syx.ca From: "M. Warner Losh" In-Reply-To: <48F4C02F.1060407@syx.ca> References: <48F4C02F.1060407@syx.ca> X-Mailer: Mew version 5.2 on Emacs 21.3 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit 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 17:02:05 -0000 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'm worried about reliability and degradation of the cf, so to get : around this I'm looking at using an external usb hard drive or memory : stick (I have 2 usb ports on my embedded devices, its a pcengines alix2c3) : : Is this a methodology most people use? or is simply buying a larger : compact flash card the recommended approach. 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. We also had a 'fail safe' tarball on the read-only part of the media that would revert the box to a default state that was sane in the event of data corruption on the /mod filesystem. The reason we bothered with that in one of our products was due to a FreeBSD bug in the vm that caused oddness in the mmapped file we used to store our configuration. 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). We had about one part in 100 wear out in the first year of being in the field. It was believed, but never confirmed, that many of these failures were due to static discharge when changing the part out rather than a failure of the flash cell... : 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. This leaves me to believe they are misinformed on : the technology or the white paper is wrong. They are misinformed. Very misinformed. Given how cheap CF cards are these days, it is cheap insurance for them to do a 'write once' with their pictures. Since their living is critically dependent on every picture being perfect, I can see their paranoia. Especially if there's a step that involves taking the flash from the camera and putting it into a reader. The more times you do this, the greater the chance for a static event to damage the part. On the other hand, my main console server is running off a SD part that's been through the wash three times (bad habit of mine: leaving these things in my jeans and not checking the pockets carefully enough). : If someone could provide further information or recommendations that : would be greatly appreciated. Hope this helps. Warner