From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757380AbZHZNkr (ORCPT ); Wed, 26 Aug 2009 09:40:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757334AbZHZNkq (ORCPT ); Wed, 26 Aug 2009 09:40:46 -0400 Received: from bee.hiwaay.net ([216.180.54.11]:39990 "EHLO bee.hiwaay.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757292AbZHZNkq (ORCPT ); Wed, 26 Aug 2009 09:40:46 -0400 Date: Wed, 26 Aug 2009 08:40:45 -0500 From: Chris Adams To: Theodore Tso Cc: linux-kernel@vger.kernel.org Subject: Re: [patch] document flash/RAID dangers Message-ID: <20090826134045.GA1516467@hiwaay.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090826124058.GK32712@mit.edu> User-Agent: Mutt/1.4i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Once upon a time, Theodore Tso said: >Well, the softwar raid layer could be improved so that it implements >scrubbing by default (i.e., have the md package install a cron job to >implement a periodict scrub pass automatically). Fedora 11 added a cron job to kick off a RAID check for each Linux MD RAID array every week. Combined with running mdmonitor, root will get an email on any failure. The other thing about this thread is that the only RAID implementation that is being discussed here is the MD RAID stack. There are a lot of RAID implementations that have the same issues: - motherboard (aka "fake") RAID - In Linux this is typically mapped with device mapper via dmraid; AFAIK there is not a tool to scrub (or even monitor the status of and notify on failure) a Linux DM RAID setup. - hardware RAID cards without battery backup - these have the exact same issues because they cannot guarantee all writes complete, nor can they keep track of incomplete writes across power failures - hardware RAID cards _with_ battery backup but that don't periodically test the battery and have a way to notify you of battery failure while Linux is running The issues being raised here are not specific to extX, MD RAID, or Linux at all; they are problems with non-"enterprise-class" RAID setups. There's a reason enterprise-class RAID costs a lot more money than the card you can pick up at Fry's. There's no reason to document the design issues of general RAID implementations in the Linux kernel. -- Chris Adams Systems and Network Administrator - HiWAAY Internet Services I don't speak for anybody but myself - that's enough trouble.