Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261865AbUFQTQC (ORCPT ); Thu, 17 Jun 2004 15:16:02 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261925AbUFQTQB (ORCPT ); Thu, 17 Jun 2004 15:16:01 -0400 Received: from meetpoint.leesburg-geeks.org ([66.63.28.250]:65289 "EHLO meetpoint.home") by vger.kernel.org with ESMTP id S261865AbUFQTPQ (ORCPT ); Thu, 17 Jun 2004 15:15:16 -0400 Message-ID: <40D1EDB7.3030401@leesburg-geeks.org> Date: Thu, 17 Jun 2004 15:15:03 -0400 From: Ken Ryan User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030915 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Hans Reiser CC: Timothy Miller , linux-kernel@vger.kernel.org, pla@morecom.no Subject: Re: mode data=journal in ext3. Is it safe to use? References: <40D1B110.7020409@leesburg-geeks.org> <40D1C18B.1030907@techsource.com> <40D1D2F0.7080102@namesys.com> In-Reply-To: <40D1D2F0.7080102@namesys.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1864 Lines: 48 Hans Reiser wrote: > Timothy Miller wrote: > >> Doesn't Reiser4 do wear-leveling for flash? > > > No, we don't. We do have wandering logs, so it would be feasible to > code, but bitmap blocks and super blocks get written to the same > locations repeatedly. > > Actually, most compact flash devices DO do wear leveling, from what I > have heard. The ones I've seen, only sort of. They'll allocate writes from available erased pages to try to distribute their use, but if you have a disk that's, say, 70% read-only data and 30% read-write then the wear-levelling will only happen on that 30% of the disk. True wear levelling will actually scrub read-only or rarely-written data, forcing it to get off its duff so the flash cells they're sitting on can get some exercise, and give the more worn cells a rest (that scrub helps ECC fix soft errors from weak cells too). True wear-levelling is really hard, and obviously requires budgeting extra bandwidth and storage devices for safely shuffling around data that the application has no intention of moving (picture losing power in the middle of a scrub). It's not worth it for the consumer CF usage model of "take photos until the card is full, then copy them all to the PC and wipe the card clean". [Yes, I tend to see this from the inside-out: I'm actually an FPGA/ASIC weenie not a kernel hacker. One of my current projects is part of a controller chip for a solid-state storage system with ${bignum} NAND flash chips. Alas, my specialty is video and graphics, so I'm still coming up the learning curve on storage systems]. ken - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/