From owner-freebsd-fs@FreeBSD.ORG Wed Jul 11 15:32:41 2012 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 91C081065670 for ; Wed, 11 Jul 2012 15:32:41 +0000 (UTC) (envelope-from jusher71@yahoo.com) Received: from nm1-vm2.bullet.mail.ne1.yahoo.com (nm1-vm2.bullet.mail.ne1.yahoo.com [98.138.91.17]) by mx1.freebsd.org (Postfix) with SMTP id 538338FC0C for ; Wed, 11 Jul 2012 15:32:41 +0000 (UTC) Received: from [98.138.90.52] by nm1.bullet.mail.ne1.yahoo.com with NNFMP; 11 Jul 2012 15:32:35 -0000 Received: from [98.138.89.234] by tm5.bullet.mail.ne1.yahoo.com with NNFMP; 11 Jul 2012 15:32:35 -0000 Received: from [127.0.0.1] by omp1049.mail.ne1.yahoo.com with NNFMP; 11 Jul 2012 15:32:35 -0000 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 340653.30158.bm@omp1049.mail.ne1.yahoo.com Received: (qmail 79535 invoked by uid 60001); 11 Jul 2012 15:32:35 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s1024; t=1342020755; bh=Jq+Lv/Wu/g53PdamkEVGhHaxQLOQ7aHLO2F2ni7OGEk=; h=X-YMail-OSG:Received:X-Mailer:Message-ID:Date:From:Subject:To:Cc:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding; b=KzMKm7/XN1ac4RcF624bjXFa/m8s4QEQ8JeIDzwlIaZtm5PxYMhLsC3LSqWDe2rfXmTQjHPFGHuqXlI31N6u2szdF9cIRLSYpWAycc0ibaHRj1zZ9nGCIpp4TNvQiCWu0UTNLvjW7Fbw/1iCxD3SXUncEK5J0Ioz411Ge/gmR6M= DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Mailer:Message-ID:Date:From:Subject:To:Cc:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding; b=2B/fahkEutQFz0+oW683OxA5H11Y7uwh8cpYuaVzaE3hGeGXygG4Rkipw58lqCiR/Or+SuNduZDGF8Y2SF1BpOyQagmODAdlZYyvpe8YRRQWzlyd7SOlqhS/cc4kGCYHETp+TPjIHV4+LQt11HygzGsIdpD8uEArDzWTQjgumBE=; X-YMail-OSG: eFivrcsVM1kUXgUF9zYfQUu3cxDdVhkEQ2UlSnlzN8dQ6pp vS8Vh9BMQy7qHrVLN5MSTD0OaenNmgqKMzOMYZCqNPubVODAT_AJRTOQNEnt 1LQ9K.0HPUdaFB4ikPo_NWMAH5_4CqSW9p3rEJA6LtHd.IoOv2YMsDQ06vFR Jm7b4zZ4HV9cwc.2tQI6TVJedvXdMUz5EbKIXDoY4UpSYfztUBqDGKaqBoGd nNF7BZhulVIPK_MXOiIkrptl4jMwSjoOvy9Uvtn6pUWkKw37MJzyJftwUUjc V3XstsiWbnrohggEsckN8dwXOg9MT8QuMm6Euq.qYd.9goBqDL8.EPPjxW91 TM4VRJTU1pLjHeE2KZsTrRC2btGlaN2IhTYQSceaQanD3rKJDVNnRIK5Q5tW Yq2i2K.UXts9H.jInOI46H6ND2RtLyk9MKRiHrHybIC_ZVUplFOBwZXyXEFe Ki10x9gW9o1C9CkMVqIkcH1wxXNZxIesI8yXT1PXos6L0tx1V12zk4QJqtna W.3E- Received: from [12.202.173.2] by web122502.mail.ne1.yahoo.com via HTTP; Wed, 11 Jul 2012 08:32:34 PDT X-Mailer: YahooMailClassic/15.0.8 YahooMailWebService/0.8.120.356233 Message-ID: <1342020754.79202.YahooMailClassic@web122502.mail.ne1.yahoo.com> Date: Wed, 11 Jul 2012 08:32:34 -0700 (PDT) From: Jason Usher To: Bob Friesenhahn In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Cc: freebsd-fs@freebsd.org Subject: Re: vdev/pool math with combined raidzX vdevs... 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: Wed, 11 Jul 2012 15:32:41 -0000 =0AHi Bob,=0A=0A--- On Wed, 7/11/12, Bob Friesenhahn wrote:=0A=0A> The probabilty is indeed additive just as you say.= =A0 My=0A> point is that the fundamental integrity is offered at the=0A> vd= ev level.=A0 If a vdev fails, then the whole pool is=0A> gone.=A0 The MTTDL= calculations for various vdev=0A> topologies vary by orders of magnitude, = which tends to make=0A> the additive nature of more vdevs insignificant.=0A= =0A=0AThanks again for responding.=0A=0AI'm not going to beat this to death= , but just to summarize, if F is 2, then the corresponding data loss probab= ilities for RAID-Z1, -Z2, -Z3 are: 14.9%, 1.3%, and 0.086%.=0A=0ABut if com= bining multiple vdevs into a zpool (as opposed to maintaining a different z= pool for each raidz3 vdev) is additive, then raidz3 becomes .258%.=0A=0ASin= ce (I think) a lot of raidz3 adoption is due to folks desiring "some overki= ll" as they attempt to overcome the "disks got really big but didn't get an= y faster (for rebuilds)"[1] ... but they are losing some of that by combini= ng vdevs in a single pool.=0A=0ANot losing so much that they're back down t= o the failure rate of a single raidz*2* vdev, but they're not at the overki= ll level they thought they were at either.=0A=0AI think that's important, o= r at least worth noting...=0A=0A=0A[1] http://storagegaga.com/4tb-disks-the= -end-of-raid/