From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from main.gmane.org ([80.91.229.2] helo=ciao.gmane.org) by pentafluge.infradead.org with esmtps (Exim 4.43 #1 (Red Hat Linux)) id 1D0bkP-0000FG-Nd for linux-mtd@lists.infradead.org; Mon, 14 Feb 2005 08:38:29 +0000 Received: from list by ciao.gmane.org with local (Exim 4.43) id 1D0bhg-000408-5K for linux-mtd@lists.infradead.org; Mon, 14 Feb 2005 09:35:36 +0100 Received: from 212.130.19.66 ([212.130.19.66]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 14 Feb 2005 09:35:36 +0100 Received: from martin by 212.130.19.66 with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 14 Feb 2005 09:35:36 +0100 To: linux-mtd@lists.infradead.org From: Martin Egholm Nielsen Date: Mon, 14 Feb 2005 09:37:45 +0100 Message-ID: References: <20050206220713.D99FE15504@desire.actrix.co.nz> <20050208000532.543131604C@desire.actrix.co.nz> <4209AAC3.2090806@magellan-technology.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit In-Reply-To: <4209AAC3.2090806@magellan-technology.com> Sender: news Subject: Re: Writing frequently to NAND - wearing, caching? List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hi Aras, >>>>> I have an application which may need to write states frequently to my >>>>> nand-fs in order to have these states in case of powerdown. >>>>> But I'm a bit concerned about wearing the nand if I write to >>>>> frequently. > > >> (because we're not using explicite wear levelling) we still have only >> reached 24,000 - only 24% of the 100,000 cycle lifetime of the flash. Thanks for the "comments" below - they are nice to have... > ... and then there is the fact that the 100,000 write cycle limit is > generally a conservative estimate based on testing of the device at an > operating temperature of around 125 celcius! Most likely the device will > be able to withstand over to 1,000,000 write cycles before failure. If > your FS uses write verification to make sure the data is secure then you > shouldn't have any problems even if you do reach this limit on some > areas of the Flash. > > From the "Toshiba NAND Flash Applications Design Guide" > > "NOR Flash is typically limited to around 100,000 cycles. Since the > electron flow-path due to the hot electron injection for programming is > different from the one due to tunneling from the floating gate to the > source for erasing, degradation is enhanced. However, in NAND Flash, > both the programming and erasing is achieved by uniform Fowler- Nordheim > tunneling between the floating gate and the substrate. This uniform > programming and uniform erasing technology guarantees a wide cell > threshold window even after 1,000,000 cycles." > > and > > "There is one question that often comes up Is ECC really necessary? > After all, the likeliest cause of a bit error is during the programming > process. For example, if you program a block, then verify it has no > errors, how reliable is the data? In these ROM-like applications where > the write/erase cycles is very low, the actual failure rate for a block > is about 3 ppm after 10 years (i.e. 3 blocks out of every million blocks > will have a bit error after 10 years) in which a block failure is > defined as a single bit error. This result was derived from testing > 29708 pieces of 512Mb NAND (0.16um) by writing a checkerboard pattern > into blocks and storing at 125C. Since there will be a non-zero data > retention failure rate, you should limit the amount of code to 1 block > to achieve a low ppm probability of failure."