Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261340AbVEaH77 (ORCPT ); Tue, 31 May 2005 03:59:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261356AbVEaH77 (ORCPT ); Tue, 31 May 2005 03:59:59 -0400 Received: from hermine.aitel.hist.no ([158.38.50.15]:36620 "HELO hermine.aitel.hist.no") by vger.kernel.org with SMTP id S261340AbVEaH75 (ORCPT ); Tue, 31 May 2005 03:59:57 -0400 Message-ID: <429C1ACD.8070600@aitel.hist.no> Date: Tue, 31 May 2005 10:05:33 +0200 From: Helge Hafting User-Agent: Debian Thunderbird 1.0.2 (X11/20050331) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Mikulas Patocka CC: Linux Kernel Mailing List Subject: Re: RAID-5 design bug (or misfeature) References: <1117454144.2685.174.camel@localhost.localdomain> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1292 Lines: 28 Mikulas Patocka wrote: > >I think that's another problem --- when RAID-5 is operating in degraded >mode, the machine must not crash or volume will be damaged (sectors >that were not written may be damaged this way). Did anybody develop some >method to care about this (i.e. something like journaling on raid)? What >do hardware RAID controllers do in this situation? > > Hot spares can keep the degraded time to a minimum. If you want to keep the risk to a minimum, unmount the raid fs until it is resynchronized. If you need more safety, there is options like raid-6 or mirrors of the entire raid-5 set. Some hw controllers have a battery-backed cache. Even a power loss won't ruin the raid - the io will simply sit in that cache until the disks become available again. The io operation that was in effect when power was lost can then be retried. Not that this saves you from everything, the fs could be inconsistent anyway due to the os being killed in the middle of its updates. A journalled fs can help with that though. Helge Hafting - 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/