From owner-freebsd-fs@FreeBSD.ORG Tue May 26 19:38:49 2009 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 9E6F91065670 for ; Tue, 26 May 2009 19:38:49 +0000 (UTC) (envelope-from artis.caune@gmail.com) Received: from mail-bw0-f213.google.com (mail-bw0-f213.google.com [209.85.218.213]) by mx1.freebsd.org (Postfix) with ESMTP id 2A1218FC1E for ; Tue, 26 May 2009 19:38:48 +0000 (UTC) (envelope-from artis.caune@gmail.com) Received: by bwz9 with SMTP id 9so4155536bwz.43 for ; Tue, 26 May 2009 12:38:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=hlgqR8WzNPAjLLsV5y4xzQPtlxbK8HHHg03MRauYRUk=; b=Gen6+mJkQ9Lf2vw9sUaeJ3xg4TsI0dzlw7I3hCw87WegvVfqCv3+Z3usF6cv6aegrm m9NQKIVaPaEMJCdDp0I7WTyny9/oJPwm25klOa66TRSsMhpobykqntfwLvUFzZj5yN2d JW0wUPhzxr0voo0KgQxPFcWp+AhzJW6OAZX24= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=XA9Lpce0TJnFOHd9676VNnVotZ+pSv00IBsI3e+KWCvApVL9Ue78gbVNjCVFzsRF/T IkC80mASnzjODEn8+oW44gU4Dzv0mdonKr2Jg9iFcvdlknhPgnfhzgTKgnCxnNqo5Y9f feDCu4AK8zPaOrPkokBVeruqD5KCq4KMyyvwI= MIME-Version: 1.0 Received: by 10.103.39.17 with SMTP id r17mr4585475muj.75.1243366727798; Tue, 26 May 2009 12:38:47 -0700 (PDT) In-Reply-To: <20090526185900.GA98171@server.vk2pj.dyndns.org> References: <9e20d71e0905230537ibcaf852g1dc32b6ffc3a681d@mail.gmail.com> <20090526185900.GA98171@server.vk2pj.dyndns.org> Date: Tue, 26 May 2009 22:38:47 +0300 Message-ID: <9e20d71e0905261238x2ff5a96cu8891f00c802a0acc@mail.gmail.com> From: Artis Caune To: peterjeremy@optushome.com.au Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: Randy Bush , freebsd-fs Subject: Re: raidz2 a bit big X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 May 2009 19:38:49 -0000 2009/5/26 : > On 2009-May-23 15:37:14 +0300, Artis Caune wrote: >>2009/5/23 Randy Bush : >>> a dozen 2tb drives in a raidz2 >>Reads on such configurations are very slow. > > Not really. =C2=A0Assuming each disk is capable of X IOPS and assuming > non-degraded mode, you can still issue (N-2)*X random reads/sec > because the parity stripes are not needed/used. =C2=A0(Compared to N*X > random reads/sec for a mirrored configuration). =C2=A0Degraded reads _are= _ > very slow because you need to read most of the spindles (I'm not sure > of the exact recovery mechanism for RAIDZ2 but it's probably close to > X random reads/sec). Not really, RAID{5,6} !=3D RAIDZ{1,2} http://blogs.sun.com/roch/entry/when_to_and_not_to http://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSRaidzReadPerformance We switched 20K mailboxes from raidz2 to mirror because of slow reads. --=20 Artis Caune Everything should be made as simple as possible, but not simpler.