From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pigeon.gentoo.org ([208.92.234.80] helo=lists.gentoo.org) by finch.gentoo.org with esmtp (Exim 4.60) (envelope-from ) id 1QHYZH-0005x6-9a for garchives@archives.gentoo.org; Wed, 04 May 2011 09:40:27 +0000 Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 9AE621C02E; Wed, 4 May 2011 09:39:02 +0000 (UTC) Received: from smtpq4.gn.mail.iss.as9143.net (smtpq4.gn.mail.iss.as9143.net [212.54.34.167]) by pigeon.gentoo.org (Postfix) with ESMTP id 423701C02E for ; Wed, 4 May 2011 09:39:02 +0000 (UTC) Received: from [212.54.34.143] (helo=smtp12.gn.mail.iss.as9143.net) by smtpq4.gn.mail.iss.as9143.net with esmtp (Exim 4.71) (envelope-from ) id 1QHYXt-0005aD-N1 for gentoo-user@lists.gentoo.org; Wed, 04 May 2011 11:39:01 +0200 Received: from 5ed02730.cm-7-1a.dynamic.ziggo.nl ([94.208.39.48] helo=data.antarean.org) by smtp12.gn.mail.iss.as9143.net with esmtp (Exim 4.71) (envelope-from ) id 1QHYXs-0007Vq-T6 for gentoo-user@lists.gentoo.org; Wed, 04 May 2011 11:39:00 +0200 Received: from localhost (localhost [127.0.0.1]) by data.antarean.org (Postfix) with ESMTP id 00A06202A for ; Wed, 4 May 2011 11:40:48 +0200 (CEST) X-Virus-Scanned: amavisd-new at antarean.org Received: from data.antarean.org ([127.0.0.1]) by localhost (data.antarean.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id kQMFJFZO6fYY for ; Wed, 4 May 2011 11:40:47 +0200 (CEST) Received: from eve.localnet (eve.lan.antarean.org [10.20.13.50]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by data.antarean.org (Postfix) with ESMTPS id A04C4107B for ; Wed, 4 May 2011 11:40:47 +0200 (CEST) From: Joost Roeleveld To: gentoo-user@lists.gentoo.org Subject: Re: [gentoo-user] mdadm and raid4 Date: Wed, 04 May 2011 11:38:59 +0200 User-Agent: KMail/4.6 beta4 (Linux/2.6.36-gentoo-r5; KDE/4.6.2; x86_64; ; ) In-Reply-To: <4DC11792.8090909@dotcomltd.ru> References: <4DC04164.8060503@dotcomltd.ru> <20110504075634.1339D1F86@data.antarean.org> <4DC11792.8090909@dotcomltd.ru> Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Message-Id: <20110504094048.00A06202A@data.antarean.org> X-ZiggoSMTP-MailScanner-Information: Please contact the ISP for more information X-ZiggoSMTP-MailScanner-ID: 1QHYXs-0007Vq-T6 X-ZiggoSMTP-MailScanner: Found to be clean X-ZiggoSMTP-MailScanner-SpamCheck: geen spam, SpamAssassin (niet cached, score=0.971, vereist 5, BAYES_20 -0.00, RDNS_DYNAMIC 0.98, T_RP_MATCHES_RCVD -0.01) X-ZiggoSMTP-MailScanner-From: joost@antarean.org X-Spam-Status: No X-Archives-Salt: X-Archives-Hash: e8b77207a55e8d96b941c4bd995eda27 On Wednesday 04 May 2011 13:08:34 Evgeny Bushkov wrote: > On 04.05.2011 11:54, Joost Roeleveld wrote: > > On Wednesday 04 May 2011 10:07:58 Evgeny Bushkov wrote: > >> On 04.05.2011 01:49, Florian Philipp wrote: > >>> Am 03.05.2011 19:54, schrieb Evgeny Bushkov: > >>>> Hi. > >>>> How can I find out which is the parity disk in a RAID-4 soft > >>>> array? I > >>>> couldn't find that in the mdadm manual. I know that RAID-4 > >>>> features a > >>>> dedicated parity disk that is usually the bottleneck of the array, > >>>> so > >>>> that disk must be as fast as possible. It seems useful to employ a > >>>> few > >>>> slow disks with a relatively fast disk in such a RAID-4 array. > >>>> > >>>> Best regards, > >>>> Bushkov E. > >>> > >>> You are seriously considering a RAID4? You know, there is a reason > >>> why > >>> it was superseded by RAID5. Given the way RAID4 operates, a first > >>> guess > >>> for finding the parity disk in a running array would be the one with > >>> the worst SMART data. It is the parity disk that dies the soonest. > >>> > >>> From looking at the source code it seems like the last specified > >>> disk is parity. Disclaimer: I'm no kernel hacker and I have only > >>> inspected the code, not tried to understand the whole MD subsystem. > >>> > >>> Regards, > >>> Florian Philipp > >> > >> Thank you for answering... The reason I consider RAID-4 is a few > >> sata/150 drives and a pair of sata II drives I've got. Let's look at > >> the problem from the other side: I can create RAID-0(from sata II > >> drives) and then add it to RAID-4 as the parity disk. It doesn't > >> bother > >> me if any disk from the RAID-0 fails, that wouldn't disrupt my RAID-4 > >> array. For example: > >> > >> mdadm --create /dev/md1 --level=4 -n 3 -c 128 /dev/sdb1 /dev/sdc1 > >> missing mdadm --create /dev/md2 --level=0 -n 2 -c 128 /dev/sda1 > >> /dev/sdd1 mdadm /dev/md1 --add /dev/md2 > >> > >> livecd ~ # cat /proc/mdstat > >> Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] > >> md2 : active raid0 sdd1[1] sda1[0] > >> > >> 20969472 blocks super 1.2 128k chunks > >> > >> md1 : active raid4 md2[3] sdc1[1] sdb1[0] > >> > >> 20969216 blocks super 1.2 level 4, 128k chunk, algorithm 0 > >> [3/2] [UU_] > >> > >> [========>............] recovery = 43.7% (4590464/10484608) > >> finish=1.4min speed=69615K/sec > >> > >> That configuration works well, but I'm not sure if md1 is the parity > >> disk here, that's why I asked. May be I'm wrong and RAID-5 is the only > >> worth array, I'm just trying to consider all pros and cons here. > >> > >> Best regards, > >> Bushkov E. > > > > I only use RAID-0 (when I want performance and don't care about the > > data), RAID-1 (for data I can't afford to loose) and RAID-5 (data I > > would like to keep). I have never bothered with RAID-4. > > > > What do you see in the "dmesg" after the mdadm commands? > > It might actually mention which is the parity disk in there. > > > > -- > > Joost > > There's nothing special in dmesg: > > md: bind > RAID conf printout: > --- level:4 rd:3 wd:2 > disk 0, o:1, dev:sdb1 > disk 1, o:1, dev:sdc1 > disk 2, o:1, dev:md2 > md: recovery of RAID array md1 > > I've run some tests with different chunk sizes, the fastest was > raid-10(4 disks), raid-5(3 disks) was closely after. Raid-4(4 disks) was > almost as fast as raid-5 so I don't see any sense to use it. > > Best regards, > Bushkov E. What's the result of: mdadm --misc --detail /dev/md1 ? Not sure what info this command will provide with a RAID-4... -- Joost