From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.nokia.com ([192.100.122.233] helo=mgw-mx06.nokia.com) by bombadil.infradead.org with esmtps (Exim 4.68 #1 (Red Hat Linux)) id 1Jxz1p-0003Dc-9j for linux-mtd@lists.infradead.org; Mon, 19 May 2008 06:39:25 +0000 Subject: Re: ext2 for read-only file system on UBI From: Artem Bityutskiy To: Hamish Moffatt In-Reply-To: <20080519062149.GA16462@cloud.net.au> References: <20080519062149.GA16462@cloud.net.au> Content-Type: text/plain; charset=utf-8 Date: Mon, 19 May 2008 09:37:53 +0300 Message-Id: <1211179073.27243.22.camel@sauron> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Cc: linux-mtd@lists.infradead.org Reply-To: dedekind@infradead.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hello Hamish, On Mon, 2008-05-19 at 16:21 +1000, Hamish Moffatt wrote: > My embedded device has a read-only root file system which is only > replaced by writing a whole image (dd, flashcp, ubiupdatevol etc). >=20 > Using gluebi and mtdblock, I think I can put a traditional block file > system (eg ext2) on top of NAND flash. What are the disadvantages of > this? (For the read-only application only.) For read-only it should be ok, although I am not sure mtdblock will like non power of 2 eraseblock sizes. But this should be trivial to fix. > Background: I've got older hardware which uses ext2 on top of compact > flash in IDE mode, and new hardware which has replaced the compact flash > with NAND. I'd like to share an ext2 image between the two if possible. Should be possible for R/O. Different sizes of eraseblocks may add extra work though. > The read-write file systems use ubifs. I'm only considering this for the > read-only volumes. One obvious disadvantage is lack of compression. Are > there others? Do I still get the reliability of ubi?=20 No, should be fine. Well, you'll still have WL across whole NAND chip, yes. You'll still have bit-flip handling. > ie what does "UBI is not an FTL" mean in practice? In practice it means that /dev/ubiX_Y are not block devices, where you may directly put ext2 and the like. --=20 Best regards, Artem Bityutskiy (=D0=91=D0=B8=D1=82=D1=8E=D1=86=D0=BA=D0=B8=D0=B9 =D0=90= =D1=80=D1=82=D1=91=D0=BC)