From owner-freebsd-stable@FreeBSD.ORG Tue Jul 26 15:20:22 2011 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B10BF1065670 for ; Tue, 26 Jul 2011 15:20:22 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from asmtpout027.mac.com (asmtpout027.mac.com [17.148.16.102]) by mx1.freebsd.org (Postfix) with ESMTP id 964878FC14 for ; Tue, 26 Jul 2011 15:20:22 +0000 (UTC) MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: text/plain; CHARSET=US-ASCII Received: from [10.1.2.163] ([173.200.187.194]) by asmtp027.mac.com (Oracle Communications Messaging Exchange Server 7u4-18.01 64bit (built Jul 15 2010)) with ESMTPSA id <0LOY003FN59L8T30@asmtp027.mac.com> for freebsd-stable@freebsd.org; Tue, 26 Jul 2011 08:20:10 -0700 (PDT) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.4.6813,1.0.211,0.0.0000 definitions=2011-07-26_05:2011-07-26, 2011-07-26, 1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 ipscore=0 suspectscore=0 phishscore=0 bulkscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx engine=6.0.2-1012030000 definitions=main-1107260106 From: Chuck Swiger In-reply-to: <4E2ED74B.9000807@dichotomia.fr> Date: Tue, 26 Jul 2011 08:20:09 -0700 Message-id: <02D59047-E03A-4259-B52F-5CD6B35E3304@mac.com> References: <4E2E9F24.1040108@dichotomia.fr> <20110726114438.GA86683@icarus.home.lan> <4E2EB814.9040704@dichotomia.fr> <20110726131655.GA88280@icarus.home.lan> <4E2ECE62.4050605@dichotomia.fr> <23BD778B-B9A4-43ED-97C6-4DF2D13F80F2@mac.com> <4E2ED74B.9000807@dichotomia.fr> To: Jerome Herman X-Mailer: Apple Mail (2.1084) Cc: freebsd-stable@freebsd.org Subject: Re: Making world but no kernel X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 Jul 2011 15:20:22 -0000 On Jul 26, 2011, at 8:03 AM, Jerome Herman wrote: > On 26/07/2011 16:58, Chuck Swiger wrote: >> On Jul 26, 2011, at 7:25 AM, Jerome Herman wrote: >>> Actually it is Raid 10 of a sort. Three first halves of the three disk concatenated and mirrored on the three second half of the same drives. >> There's a significant problem right there. Not only will that configuration badly degrade the performance of the RAID volume, it also compromises the goal of redundancy which RAID-1 is supposed to provide. >> >> Regards, > > Disk are interweaved, so the performances are quite good (about 160% of a single drive) A six-disk RAID-10 setup ought to provide nearly 600% read performance improvement and 300% of the write performance of a single drive-- real numbers tend to be perhaps 550%/250% or so. > and the redundancy is here. Any single drive can fail, and the other two will be there to provide data. Basically the first plesk is a-b-c, and the second is b-c-a, so everything should be fine. Yes, if you do that you can survive a single disk failure, but the degraded performance is going to suck, and you have no chance of surviving a second disk outage. A six-disk RAID-10 volume can survive up to 3 disks failing (although it has a 20% chance of losing the RAID with a two-disk failure and a 50% chance of losing data if a third disk goes without anyone fixing things). Regards, -- -Chuck