From owner-freebsd-questions@FreeBSD.ORG Mon Jul 22 07:11:37 2013 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id 1FDCD611 for ; Mon, 22 Jul 2013 07:11:37 +0000 (UTC) (envelope-from kraduk@gmail.com) Received: from mail-we0-x22b.google.com (mail-we0-x22b.google.com [IPv6:2a00:1450:400c:c03::22b]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id 98E082569 for ; Mon, 22 Jul 2013 07:11:36 +0000 (UTC) Received: by mail-we0-f171.google.com with SMTP id q55so1656859wes.2 for ; Mon, 22 Jul 2013 00:11:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=911sE6SewhqAC38tC9T1H/0k3/aykHujhmJvyEhvGLg=; b=wn7hzMrXAKOmEZpHr2J6RodWUrxoj4VL8HzYsDIE5snFMLEMDr743JTXHIBp3oAez/ tj96Bb9k5w7jE9nvzFUjyP3AkeK7YhRZC5IvcAydmhJEjGMaQ8O+Sby+xqDoFLgE0AfL Nd3xdxTgpHcKUvsOyP7Y669nyhSf8nQZJMfKRyOlF5/x8fiA8LlFc/RaQa1pDJp8kbnE jfFdxwQf6E8F3JVDyfe7Z5b140BUOWr7T1oGlOOzT5G3iCIu2rBe0fVe03F0Vy+IT0z1 +P5Z1yLnIJ8SR88OkMB6kqVVF2N8yKtnulEgTuZOsK33KsCTfh6e1cq+NaaAw40jhPDI zV0A== MIME-Version: 1.0 X-Received: by 10.180.10.138 with SMTP id i10mr28711134wib.53.1374477094992; Mon, 22 Jul 2013 00:11:34 -0700 (PDT) Received: by 10.216.68.137 with HTTP; Mon, 22 Jul 2013 00:11:34 -0700 (PDT) In-Reply-To: References: <4DFBC539-3CCC-4B9B-AB62-7BB846F18530@gmail.com> <976836C5-F790-4D55-A80C-5944E8BC2575@gmail.com> <51E51558.50302@ShaneWare.Biz> <51E52190.7020008@fjl.co.uk> <6CE5718E-2646-4D8C-AF98-37384B8851C5@mac.com> <51EAC56C.4030801@fjl.co.uk> <20130720201214.90206565e00675611996176d@sohara.org> Date: Mon, 22 Jul 2013 08:11:34 +0100 Message-ID: Subject: Re: to gmirror or to ZFS From: krad To: Daniel Feenberg Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.14 Cc: frank2@fjl.co.uk, Steve O'Hara-Smith , FreeBSD Questions X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 22 Jul 2013 07:11:37 -0000 But then zfs doesn't access every block on the disk does it, only the allocated ones On 20 July 2013 21:07, Daniel Feenberg wrote: > > > On Sat, 20 Jul 2013, Steve O'Hara-Smith wrote: > > On Sat, 20 Jul 2013 18:14:20 +0100 >> Frank Leonhardt wrote: >> >> It's worth noting, as a warning for anyone who hasn't been there, that >>> the number of times a second drive in a RAID system fails during a >>> rebuild is higher than would be expected. During a rebuild the remaining >>> drives get thrashed, hot, and if they're on the edge, that's when >>> they're going to go. And at the most inconvenient time. Okay - obvious >>> when you think about it, but this tends to be too late. >>> >> >> Having the cabinet stuffed full of nominally identical drives >> bought at the same time from the same supplier tends to add to the >> probability that more than one drive is on the edge when one goes. It's a >> pity there are now only two manufacturers of spinning rust. >> > > Often this is presummed to be the reason for double failures close in > time, also common mode failures such as environment, a defective power > supply or excess voltage can be blamed. I have to think that the most > common "cause" for a second failure soon after the first is that a failed > drive often isn't detected until a particular sector is read or written. > Since the resilvering reads and writes every sector on multiple disks, > including unused sectors, it can "detect" latent problems that may have > existed since the drive was new but which haven't been used for data yet, > or have gone bad since the last write, but haven't been read since. > > The ZFS scrub processes only sectors with data, so it provides only > partial protection against double failures. > > Daniel Feenberg > NBER > > > > >> -- >> Steve O'Hara-Smith >> ______________________________**_________________ >> freebsd-questions@freebsd.org mailing list >> http://lists.freebsd.org/**mailman/listinfo/freebsd-**questions >> To unsubscribe, send any mail to "freebsd-questions-** >> unsubscribe@freebsd.org " >> >> ______________________________**_________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/**mailman/listinfo/freebsd-**questions > To unsubscribe, send any mail to "freebsd-questions-** > unsubscribe@freebsd.org " >