From owner-freebsd-questions@FreeBSD.ORG Mon Jan 19 16:49:25 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 4679316A4CE for ; Mon, 19 Jan 2004 16:49:25 -0800 (PST) Received: from wonkity.com (wonkity.com [65.173.111.5]) by mx1.FreeBSD.org (Postfix) with ESMTP id 0980943D48 for ; Mon, 19 Jan 2004 16:49:24 -0800 (PST) (envelope-from wblock@wonkity.com) Received: from wonkity.com (localhost [127.0.0.1]) by wonkity.com (8.12.10/8.12.10) with ESMTP id i0K0nF1m084654; Mon, 19 Jan 2004 17:49:15 -0700 (MST) (envelope-from wblock@wonkity.com) Received: from localhost (wblock@localhost) by wonkity.com (8.12.10/8.12.10/Submit) with ESMTP id i0K0nFCF084651; Mon, 19 Jan 2004 17:49:15 -0700 (MST) (envelope-from wblock@wonkity.com) Date: Mon, 19 Jan 2004 17:49:15 -0700 (MST) From: Warren Block To: "Cordula's Web" In-Reply-To: <20040119074947.28D7440854@fw.farid-hajji.net> Message-ID: <20040119172643.S84590@wonkity.com> References: <007701c3ddaf$8c58f000$8b01010a@nyalaptopen> <1074484137.21654.7.camel@tux> <20040119074947.28D7440854@fw.farid-hajji.net> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII cc: freebsd-questions@freebsd.org Subject: Re: [was: Cutting the power ... ] Journaling file system 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: Tue, 20 Jan 2004 00:49:25 -0000 On Mon, 19 Jan 2004, Cordula's Web wrote: > Beware when using flash ram as some kind of live filesystem! > Flash media has a quite limited number of erase cycles > You may think that's plenty, but since filesystem meta-data > is often written at the same location (superblocks etc...), > this location will quickly reach the threshold, where it > can't be used anymore! Current flash memory spreads the writes around through "wear leveling." A logical write to an address is remapped internally to keep the wear as even as possible. There's a kind of neat calculator at: http://www.m-sys.com/content/Developer/Calc.asp There's also a PDF from the same company that talks about how it works, but I couldn't find it on their web site, so: http://www.spezial.de/commercio/dateien/magazin/FFD_Life_Expectancy.pdf -Warren Block * Rapid City, South Dakota USA