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 1QHYu6-0008Su-0W for garchives@archives.gentoo.org; Wed, 04 May 2011 10:01:58 +0000 Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 839A01C02E; Wed, 4 May 2011 10:00:34 +0000 (UTC) Received: from mail.dotcomltd.ru (dotcomltd.ru [89.21.149.49]) by pigeon.gentoo.org (Postfix) with ESMTP id 1F7EC1C02E for ; Wed, 4 May 2011 10:00:34 +0000 (UTC) Received: by mail.dotcomltd.ru (Mail server, from userid 5002) id 62EC263E8B2; Wed, 4 May 2011 14:00:33 +0400 (MSD) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on phoenix.dotcomltd.ru X-Spam-Level: X-Spam-Status: No, score=-2.9 required=4.5 tests=ALL_TRUSTED,BAYES_00, T_RP_MATCHES_RCVD autolearn=ham version=3.3.1 Received: from [192.168.0.10] (zhen.dotcomltd.ru [192.168.0.10]) by mail.dotcomltd.ru (Mail server) with ESMTPSA id 2D59F63E884 for ; Wed, 4 May 2011 13:59:57 +0400 (MSD) Message-ID: <4DC1239C.3030202@dotcomltd.ru> Date: Wed, 04 May 2011 13:59:56 +0400 From: Evgeny Bushkov User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.15) Gecko/20110309 Lightning/1.0b2 Thunderbird/3.1.9 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 To: gentoo-user@lists.gentoo.org Subject: Re: [gentoo-user] mdadm and raid4 References: <4DC04164.8060503@dotcomltd.ru> <20110504075634.1339D1F86@data.antarean.org> <4DC11792.8090909@dotcomltd.ru> <20110504094048.00A06202A@data.antarean.org> In-Reply-To: <20110504094048.00A06202A@data.antarean.org> X-Enigmail-Version: 1.1.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Archives-Salt: X-Archives-Hash: f5fd608e51bab0e3e5abc79f3545a30d On 04.05.2011 13:38, Joost Roeleveld wrote: > 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... > > -- > Joostlivecd ~ # mdadm --misc --detail /dev/md1 livecd ~ # mdadm --misc --detail /dev/md1 /dev/md1: Version : 1.2 Creation Time : Wed May 4 13:54:33 2011 Raid Level : raid4 Array Size : 122624 (119.77 MiB 125.57 MB) Used Dev Size : 61312 (59.89 MiB 62.78 MB) Raid Devices : 3 Total Devices : 3 Persistence : Superblock is persistent Update Time : Wed May 4 13:55:14 2011 State : clean Active Devices : 3 Working Devices : 3 Failed Devices : 0 Spare Devices : 0 Chunk Size : 128K Name : livecd:1 (local to host livecd) UUID : 654218f0:9f0b88d5:d82f39bc:ae08aa1e Events : 19 Number Major Minor RaidDevice State 0 8 17 0 active sync /dev/sdb1 1 8 33 1 active sync /dev/sdc1 3 9 2 2 active sync /dev/md2 Best regards, Bushkov E.