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 1QHbU9-0000ol-U7 for garchives@archives.gentoo.org; Wed, 04 May 2011 12:47:22 +0000 Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 9EA2A1C029; Wed, 4 May 2011 12:46:01 +0000 (UTC) Received: from out2.smtp.messagingengine.com (out2.smtp.messagingengine.com [66.111.4.26]) by pigeon.gentoo.org (Postfix) with ESMTP id 673931C029 for ; Wed, 4 May 2011 12:46:01 +0000 (UTC) Received: from compute4.internal (compute4.nyi.mail.srv.osa [10.202.2.44]) by gateway1.messagingengine.com (Postfix) with ESMTP id 2711B201A2 for ; Wed, 4 May 2011 08:46:01 -0400 (EDT) Received: from frontend1.messagingengine.com ([10.202.2.160]) by compute4.internal (MEProxy); Wed, 04 May 2011 08:46:01 -0400 DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d=messagingengine.com; h=message-id:date:from:mime-version:to:subject:references:in-reply-to:content-type; s=smtpout; bh=7jNtpNljXDfks5hXaFTE87+B3nI=; b=XDAgb+cuFhDSRpSFvzgtqNfrPpye1R+wwRv5PlWIMU7iVaAcj9YJ8AovyPE0PX0+twPSu1+oITJ5EeAK0aPaiW8Szztyhr31pAw02VN64wSB6FraS6T8N2rnwOTGWBtM/GuFH52kurUE7yUCp60U9k0N/s5YkqkrKuSPDWo1in0= X-Sasl-enc: KVgM+UrGoNIOq2nkPLFRetdVxXztP5gMf/0OhxzpSq2v 1304513159 Received: from [192.168.5.18] (serv.binarywings.net [83.169.5.6]) by mail.messagingengine.com (Postfix) with ESMTPSA id 711F1404B9B for ; Wed, 4 May 2011 08:45:59 -0400 (EDT) Message-ID: <4DC14A83.4060706@binarywings.net> Date: Wed, 04 May 2011 14:45:55 +0200 From: Florian Philipp User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.15) Gecko/20110313 Lightning/1.0b3pre 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> <4DC0786B.6010600@binarywings.net> <4DC0ED3E.8070509@dotcomltd.ru> <20110504075634.1339D1F86@data.antarean.org> <4DC11792.8090909@dotcomltd.ru> <4DC14908.50301@binarywings.net> In-Reply-To: <4DC14908.50301@binarywings.net> X-Enigmail-Version: 1.1.2 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigBF8C7CB71F94E8795C6361A3" X-Archives-Salt: X-Archives-Hash: 91d9eed4bc89888ba97012f1fcc53455 This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigBF8C7CB71F94E8795C6361A3 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Am 04.05.2011 14:39, schrieb Florian Philipp: > Am 04.05.2011 11:08, schrieb Evgeny Bushkov: >> 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 featur= es 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 g= uess >>>>> for finding the parity disk in a running array would be the one wit= h 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 di= sk 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 a= t >>>> 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 bot= her >>>> me if any disk from the RAID-0 fails, that wouldn't disrupt my RAID-= 4 >>>> array. For example: >>>> >>>> mdadm --create /dev/md1 --level=3D4 -n 3 -c 128 /dev/sdb1 /dev/sdc1 = missing >>>> mdadm --create /dev/md2 --level=3D0 -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_] >>>> [=3D=3D=3D=3D=3D=3D=3D=3D>............] recovery =3D 43.7% (4590464= /10484608) finish=3D1.4min >>>> speed=3D69615K/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 on= ly >>>> 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 d= ata),=20 >>> RAID-1 (for data I can't afford to loose) and RAID-5 (data I would li= ke to=20 >>> keep). I have never bothered with RAID-4. >>> > [...] >> >> 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) w= as >> almost as fast as raid-5 so I don't see any sense to use it. >> >> Best regards, >> Bushkov E. >> >> >> >=20 > When you have an array with uneven disk speeds, you might consider usin= g > the --write-mostly option of mdadm: > -W, --write-mostly > subsequent devices lists in a --build, --create, or --add command > will be flagged as 'write-mostly'. This is valid for RAID1 only and > means that the 'md' driver will avoid reading from these devices if at > all possible. This can be useful if mirroring over a slow link. >=20 > This should help in concurrent read and write operations because the > kernel will not dispatch read requests to a disk that is already having= > trouble managing the write operations. >=20 > On another point: Are you sure your disks have different speeds? SATA15= 0 > and 300 are no reliable indicator because most HDDs cannot saturate the= > SATA port anyway. dd is still the most reliable way to measure > sequential throughput. >=20 > Regards, > Florian Philipp >=20 `man 4 md` also states that the "the last of the active devices in the array" is the parity disk in a RAID4. Regards, Florian Philipp --------------enigBF8C7CB71F94E8795C6361A3 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.17 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk3BSoMACgkQqs4uOUlOuU9fmACeMS4EbbevSGQx5IPaU5/tDsmV abgAn0o/PmQGxMY3T4CStSzqibxX9689 =JkoT -----END PGP SIGNATURE----- --------------enigBF8C7CB71F94E8795C6361A3--