From owner-freebsd-questions@FreeBSD.ORG Fri Aug 8 17:54:22 2014 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id A678428E for ; Fri, 8 Aug 2014 17:54:22 +0000 (UTC) Received: from mail-qg0-f48.google.com (mail-qg0-f48.google.com [209.85.192.48]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 5ED252477 for ; Fri, 8 Aug 2014 17:54:21 +0000 (UTC) Received: by mail-qg0-f48.google.com with SMTP id i50so6296584qgf.21 for ; Fri, 08 Aug 2014 10:54:20 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:mime-version:content-type:from :in-reply-to:date:cc:content-transfer-encoding:message-id:references :to; bh=hshISUT8qXOw41BKe9UKn3k+y1z0EFFg9Dx1aej0yhU=; b=DjFsdkwfYtW8epc2abwYsRk7iI/Dy4kRESIu8kfrThkKTm2YyQEro/LkvsVRhSrqaC XCvlwZCUe3VuNEDioQ3/8x1tFMQ4nNJqPiXKD91cq35P/qu0qbiu6Y1VfvlbiBuHrfw5 BckIKNhFr6V/VYf/b9UPj1lKGB37ugV8xX4MmrbBJOpoW0TENk+WBtolC14JMqgu/9po DSHKxAMdy67P2L09jJJFpXSgl0xMuXXkpxIkOGnu5a56PLLDaRID8hZvNHPjvUx0mTf/ YeB6vARoNonIb/90y/Xy4ddoEnjjDay/Kwl+Lw+7Q3Vnbq+R/HDplcbL34LGy1LhedPe eXxg== X-Gm-Message-State: ALoCoQn8tsjayKVlGyiqGjFG+6DFZ1QJfTgZzOVjM1/xHQWch1hh7ij2CW2scD/xnzG6jgHX5PeL X-Received: by 10.229.57.138 with SMTP id c10mr6701078qch.30.1407520460512; Fri, 08 Aug 2014 10:54:20 -0700 (PDT) Received: from [192.168.1.127] (c-71-234-255-65.hsd1.vt.comcast.net. [71.234.255.65]) by mx.google.com with ESMTPSA id x5sm6594912qaj.42.2014.08.08.10.54.19 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 08 Aug 2014 10:54:19 -0700 (PDT) Subject: Re: gvinum raid5 vs. ZFS raidz Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=windows-1252 From: Paul Kraus In-Reply-To: <201408071106.s77B6JCI005742@sdf.org> Date: Fri, 8 Aug 2014 13:54:18 -0400 Content-Transfer-Encoding: quoted-printable Message-Id: <5B99AAB4-C8CB-45A9-A6F0-1F8B08221917@kraus-haus.org> References: <201408020621.s726LsiA024208@sdf.org> <53DCDBE8.8060704@qeng-ho.org> <201408060556.s765uKJA026937@sdf.org> <53E1FF5F.1050500@qeng-ho.org> <201408070831.s778VhJc015365@sdf.org> <201408070936.s779akMv017524@sdf.org> <201408071106.s77B6JCI005742@sdf.org> To: Scott Bennett , FreeBSD Questions !!!! X-Mailer: Apple Mail (2.1878.6) Cc: freebsd@qeng-ho.org, Trond.Endrestol@fagskolen.gjovik.no X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 08 Aug 2014 17:54:22 -0000 On Aug 7, 2014, at 7:06, Scott Bennett wrote: > Even just as parity bits, those would amount to only one bit per > eight bytes, which seems inadequate. OTOH, the 520 bytes thing is > tickling something in my memory that I can't quite seem to recover, = and > I don't know (or can't remember) what else those eight bytes might be > used for. In any case, at the time I spoke with the guy at = Seagate/Samsung, > I was unaware of the server grade vs. non-server grade distinction, = so I > didn't know to ask him anything about whether silent errors should be > accepted as "normal" for the server grade of disks. Take a look at the manufacturer data sheets for this drives. All of the = ones that I have looked at over the past ten years have included the = =93uncorrectable error rate=94 and it is generally 1 in 10e-14 for = =93consumer grade drives=94 and 1 in 1e-15 for =93enterprise grade = drives=94. That right there shows the order of magnitude difference in = this error rate between consumer and enterprise drives. The reason no one even discussed it prior to the appearance of 1TB = drives is that over the life of a less than 1TB drive you are = statistically almost assured of NOT running into it. It was still there, = but no one wrote/read enough data over the life of the drive to hit it. On the other hand, I am willing to bet that many of the =93random=94 = systems crashes (and Windows BSOD) were caused by this issue. A hard = disk returned a single bit error in a bad place and the system crashed. Note that all disk drives include some amount of error checking, even as = far back as the 10MB MFM drives of the 1980=92s. Anyone remember having = to manually manage the =93Bad block list=94 ? Those were blocks that = were so bad that the error correction could not fix them. But, as far as = I can tell, the uncorrectable errors have always been with us, we just = did not not see them. -- Paul Kraus paul@kraus-haus.org