From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from skyhigh.actrix.co.nz ([203.96.16.175]) by canuck.infradead.org with esmtp (Exim 4.54 #1 (Red Hat Linux)) id 1F9Zb3-0006SP-Ik for linux-mtd@lists.infradead.org; Wed, 15 Feb 2006 22:14:24 -0500 From: Charles Manning To: linux-mtd@lists.infradead.org Date: Thu, 16 Feb 2006 16:17:04 +1300 References: <200602091126.10462.manningc2@actrix.gen.nz> <200602141510.12749.wolfgang.mues@auerswald.de> In-Reply-To: <200602141510.12749.wolfgang.mues@auerswald.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200602161617.04905.manningc2@actrix.gen.nz> Cc: Wolfgang =?iso-8859-15?q?M=FCes?= Subject: Re: Questions about NAND (double)bit errors List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wednesday 15 February 2006 03:10, Wolfgang M=FCes wrote: > Hello Charles, > > Charles Manning wrote: > > * YAFFS is very conservative on dealing with ECC failures. YAFFS retires > > a block if one ECC failure is seen. JFFS2, IIRC allows five of so failu= re > > before retiring a block. The Toshiba folk have told me that if a block = is > > going bad, it is most likely to start displaying recoverable 1-bit erro= rs > > before displaying non-recoverable multi-bit errors. Thus, YAFFS will > > potentially perform differently in this area. > > About bad block detection: what is your oppinion about partitioning the > flash (the programs in a read-only partition, the data in r/w). This gets fs specific. With YAFFS (and I assume JFFS2, but consult an exper= t),=20 grabage collection will force read-only files to get rewritten occasionally= =2E=20 Thus for ultimate reliability it is probably a GoodIdea to seperate the=20 read-only stuff into a seperate partition. This is also a GoodIdea in that = a=20 smaller partition mounts faster (true for YAFFS and JFFS2). So if all your= =20 kernel + mount stuff is seperated from your rw stuff things will probably d= go=20 better. > > How about detection of ECC errors in read only partitions? ECC should be done on both rw and read-only partitions. Sometimes NAND gets= =20 read disturbs which would impact on read-only partitions. Also, write=20 disturbs from writes to one partition can still corrupt a read-only partiti= on=20 on the same chip. > > > One important factor, IMHO, is how you handle the write protect pin on > > the NAND. Some people tie the WP to the power supply failure flag. IMHO > > this is a bad thing to do since it can cause incomplete writes to happen > > if the wp is asserted during a write or erase cycle. > > I have checked this. > > WP is tied to VCC, and VCC is stable at least 500ms after a power fail > detect. 500ms is long enough to grow a beard. There's been some interesting discussion over in yaffs-land on this. If you= =20 don't subscribe to yaffs list then you can catch up on the yaffs archive. =2D- Charles