From owner-freebsd-stable@FreeBSD.ORG Wed Apr 16 12:27:18 2003 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 4B45D37B401 for ; Wed, 16 Apr 2003 12:27:18 -0700 (PDT) Received: from lurza.secnetix.de (lurza.secnetix.de [212.66.1.130]) by mx1.FreeBSD.org (Postfix) with ESMTP id 390ED43F75 for ; Wed, 16 Apr 2003 12:27:17 -0700 (PDT) (envelope-from olli@lurza.secnetix.de) Received: from lurza.secnetix.de (lejqdo@localhost [127.0.0.1]) by lurza.secnetix.de (8.12.8p1/8.12.8) with ESMTP id h3GJRFB5015917 for ; Wed, 16 Apr 2003 21:27:16 +0200 (CEST) (envelope-from oliver.fromme@secnetix.de) Received: (from olli@localhost) by lurza.secnetix.de (8.12.8p1/8.12.8/Submit) id h3GJRFWw015916; Wed, 16 Apr 2003 21:27:15 +0200 (CEST) Date: Wed, 16 Apr 2003 21:27:15 +0200 (CEST) Message-Id: <200304161927.h3GJRFWw015916@lurza.secnetix.de> From: Oliver Fromme To: freebsd-stable@FreeBSD.ORG In-Reply-To: X-Newsgroups: list.freebsd-stable User-Agent: tin/1.5.4-20000523 ("1959") (UNIX) (FreeBSD/4.8-RELEASE (i386)) MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Subject: Re: PATCH: Forcible delaying of UFS (soft)updates X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list Reply-To: freebsd-stable@FreeBSD.ORG List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 16 Apr 2003 19:27:18 -0000 Chris Dillon wrote: > On Wed, 16 Apr 2003, Terry Lambert wrote: > > [Flash memory] > > The life expectancy of these devices is really, really > > underestimated. In practice, I've seen two million write cycles > > from some of these in lab machines which get rewritten pretty often. > > I realize they have what looks like a really big number of writes on a > human scale, but to a computer which does things methodically day in > and day out without stopping, those writes can add up relatively > quickly. Even with a life of two million write cycles, the > "occasional" 30-second round of updates that happen to write the same > bits over and over The controller in things such as CompactFlash cards will _not_ write the same physical bits over and over. Those beasts are clever enough to remap logical blocks to different physical blocks upon each write access, so that the written-to flash cells are evenly distributed over the whole physical range. You can probably update the atime of files 100 million times and more without any problems, because all of those 100 million writes will end up on all different flash blocks. Of course, that's provided that there are also areas in your filesystem which are less frequently written to, but that's usually the case (how often do you rewrite binaries and libs?). So I agree with Terry that the life expectancy of flash devices really underestimated. Regards Oliver -- Oliver Fromme, secnetix GmbH & Co KG, Oettingenstr. 2, 80538 München Any opinions expressed in this message may be personal to the author and may not necessarily reflect the opinions of secnetix in any way. "If you do things right, people won't be sure you've done anything at all." -- God in Futurama season 4 episode 8