From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lazybastard.de ([212.112.238.170] helo=longford.lazybastard.org) by canuck.infradead.org with esmtps (Exim 4.63 #1 (Red Hat Linux)) id 1HQXhd-0006ib-TT for linux-mtd@lists.infradead.org; Sun, 11 Mar 2007 19:43:52 -0400 Date: Mon, 12 Mar 2007 00:40:31 +0100 From: =?utf-8?B?SsO2cm4=?= Engel To: Sam Ravnborg Subject: Re: MTD_PHRAM - what filesystem to use? Message-ID: <20070311234031.GC17463@lazybastard.org> References: <20070311200508.GA3362@uranus.ravnborg.org> <20070311203122.GB17463@lazybastard.org> <20070311210835.GA3794@uranus.ravnborg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20070311210835.GA3794@uranus.ravnborg.org> Cc: linux-mtd@lists.infradead.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, 11 March 2007 22:08:35 +0100, Sam Ravnborg wrote: > > > > Write rate is 10kB / 10s * 1.1 = 1.1kB/s. > > Total written data in 10a is: 1.1kB/s * 31536000s/a * 10a = 346GB > > Required flash size: 346GB / 100k = 3468kB > > I assume that from a performance point-of-view the FLASH based version > suffer more than the RAM one - since it is simple to 'erase' RAM. Not likely. With the example numbers, 1.1kB/s will be peanuts compared to flash write bandwidth. Erases happen ahead-of-time in JFFS2, so those won't matter much either. Reads won't matter at all, if you are looking at 100kB or so - all of that can easily be cached. If you require a significantly higher write bandwidth, the required flash size will equally increase. Who knows, battery backed RAM may be cheaper than flash due to the required size before the bandwidth becomes a problem. Good luck with your design, Sam! Jörn -- If you're willing to restrict the flexibility of your approach, you can almost always do something better. -- John Carmack