From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dell-paw-3.cambridge.redhat.com ([195.224.55.237] helo=passion.cambridge.redhat.com) by pentafluge.infradead.org with esmtp (Exim 3.22 #1 (Red Hat Linux)) id 18KFSP-00045s-00 for ; Fri, 06 Dec 2002 10:11:41 +0000 From: David Woodhouse In-Reply-To: <049e01c29d0f$b3c52ff0$221faf9d@iphase.com> References: <049e01c29d0f$b3c52ff0$221faf9d@iphase.com> To: "Chantara Thlang" Cc: linux-mtd@lists.infradead.org Subject: Re: need arguments to use JFFS2 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Fri, 06 Dec 2002 10:42:11 +0000 Message-ID: <28792.1039171331@passion.cambridge.redhat.com> Sender: linux-mtd-admin@lists.infradead.org Errors-To: linux-mtd-admin@lists.infradead.org List-Help: List-Post: List-Subscribe: , List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: thlang@iphase.com said: > Please could someone give me some arguments to use JFFS2 instead of > all others Flash FS such as CRAMFS ? cramfs is read-only. If you don't want to write to your file system, you should probably be using it instead of JFFS2. The only other flash file system for Linux is YAFFS, for use on NAND flash. I don't know as much about YAFFS as I should -- the choice between YAFFS and JFFS2 on NAND is basically a tradeoff between the improved speed and mount time of YAFFS, and the increased storage capacity which JFFS2 compression gives, I think. Charles will probably offer more enlightenment. Other than that, you only have the brain-dead 'translation layer' crap which is a kind of journalling pseudo-filesystem used to emulate a virtual hard drive, on which you need to use put a 'normal' journalling file system. This two-layer approach made some sense in the days of DOS, where you could just provide an INT 13h Disk BIOS IRQ handler and pretend to be a normal hard drive to DOS, but it makes far less sense now. You end up with power-loss safety being implemented in _both_ your 'normal' file system and the underlying pseudo-fs, the pseudo-fs has no way of knowing which blocks on the virtual hard drive are marked as 'free' by the higher file system and so it keep garbage-collecting stale data from one place on the flash to another, and at least at the moment, it means you don't get compression -- although that's not a fundamental design flaw like the others. -- dwmw2