From owner-freebsd-hackers@FreeBSD.ORG Mon Jun 1 13:19:53 2009 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 2FA47106564A for ; Mon, 1 Jun 2009 13:19:53 +0000 (UTC) (envelope-from kraduk@googlemail.com) Received: from mail-ew0-f212.google.com (mail-ew0-f212.google.com [209.85.219.212]) by mx1.freebsd.org (Postfix) with ESMTP id A25DE8FC26 for ; Mon, 1 Jun 2009 13:19:52 +0000 (UTC) (envelope-from kraduk@googlemail.com) Received: by ewy8 with SMTP id 8so4341858ewy.43 for ; Mon, 01 Jun 2009 06:19:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:received:received:from:to:cc:references:subject :date:message-id:mime-version:content-type:content-transfer-encoding :x-mailer:in-reply-to:x-mimeole:thread-index; bh=SkE8t34XmH3jpYjotPKYMY8n7oUYjPRN2iyTOk89bxg=; b=w5xg6LnRj/5Kdyuh3/JntMXi0MaepEXpQ7seFUCqF0IFOUMdZdwcOV2OFkwOFRld04 i9a0nHqrcluVzzRQvCEejzlvvJagYMoEnpCo46Y61AwFzLYAb7x0K/08aFo/YrM1YYOV 1Y40r80PSRS0xcpZcULZyRdGX7pGy0asW+rKE= DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=from:to:cc:references:subject:date:message-id:mime-version :content-type:content-transfer-encoding:x-mailer:in-reply-to :x-mimeole:thread-index; b=yBreGJuyDn7ok1YfrnhyXwQymL/ocqKTO/DcDge8KMGbbLEwA3UqSIY0yweJNjtmO+ E12WogK02pCwn86uKQXZA96e/XWpkb3IOrBmPeMFkQBeuQWpIJe5u0XGAaTaCp8AdyVI l8fALF1WF+sx87WvxdSe6bg5j8Fkpq4EoKAvw= Received: by 10.210.57.12 with SMTP id f12mr6172326eba.46.1243862391539; Mon, 01 Jun 2009 06:19:51 -0700 (PDT) Received: from LTPCSCOTT (e1-1.ns500-1.ts.milt.as9105.net [212.74.112.53]) by mx.google.com with ESMTPS id 4sm7047579ewy.56.2009.06.01.06.19.50 (version=SSLv3 cipher=RC4-MD5); Mon, 01 Jun 2009 06:19:51 -0700 (PDT) From: krad To: "'Tom Evans'" , "'krad'" References: <20090530175239.GA25604@logik.internal.network> <20090530144354.2255f722@bhuda.mired.org> <20090530191840.GA68514@logik.internal.network> <20090530162744.5d77e9d1@bhuda.mired.org> <20090531201445.GA82420@logik.internal.network> <0229B3BF1BE94C82AA11FD06CBE0BDEF@uk.tiscali.intl> <20090531235943.GA77374@logik.internal.network> <3346D963EE2E4D28AE89CB71C2F92939@uk.tiscali.intl> <1243860612.9871.68.camel@strangepork.london.mintel.ad> Date: Mon, 1 Jun 2009 14:19:50 +0100 Message-ID: <20754E8E3F5940E0875AD0BC76A78BAB@uk.tiscali.intl> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Office Outlook 11 In-Reply-To: <1243860612.9871.68.camel@strangepork.london.mintel.ad> X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Thread-Index: Acnit4Lphf0Wb+xbQpu5en6RrgTu0wAAp9Pg X-Mailman-Approved-At: Mon, 01 Jun 2009 13:59:48 +0000 Cc: freebsd-hackers@freebsd.org, xorquewasp@googlemail.com Subject: RE: Request for opinions - gvinum or ccd? X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 01 Jun 2009 13:19:53 -0000 no you would only loose the data for that block. Zfs also checksums meta data, but by default keeps multiple copies of it so that's fairly resilient. If you had the copies set to > 1 then you wouldn't loose the block either, unless you were real unlucky. It's just about pushing the odds back further and further. If you are super paranoid by all means put in 48 drive, group them into 5 x 8 drive raidz2 vdevs, have a bunch of hot spares, and enable copies=5 for blocks and metadata, then duplicate the system and put the other box on another continent and zfs send all you updates every 15 mins via a private deadicated. This will all prove very resilient, but you will get very little % storage from your drives, and have quite a large bandwidth bill 8) Oh and don't forget the scrub you disk regularly. BTW that would rebuild any missing copies as well (eg if you increase the number of copies after data is stored on the fs) -----Original Message----- From: Tom Evans [mailto:tevans.uk@googlemail.com] Sent: 01 June 2009 13:50 To: krad Cc: xorquewasp@googlemail.com; freebsd-hackers@freebsd.org Subject: RE: Request for opinions - gvinum or ccd? On Mon, 2009-06-01 at 09:32 +0100, krad wrote: > Zfs has been designed for highly scalable redundant disk pools therefore > using it on a single drive kind of goes against it ethos. Remember a lot of > the blurb in the man page was written by sun and therefore is written with > corporates in mind, therefore the cost with of the data vs an extra drive > being so large why wouldn't you make it redundant. > > Having said that sata drives are cheap these days so you would have to be on > the tightest of budgets not to do a mirror. > > Having said all this we quite often us zfs on a single drive, well sort of. > The sun clusters have external storage for the shared file systems. These > are usually a bunch of drives, raid 5, 10 or whatever. Then export a single > lun, which is presented to the various nodes. There is a zpool created on > this LUN. So to all intents and purposes zfs thinks its on a single drive > (the redundancy provided by the external array). This is common practice and > we see no issues with it. By doing this surely you lose a lot of the self healing that ZFS offers? For instance, if the underlying vdev is just a raid5, then a disk failure combined with an undetected checksum error on a different disk would lead you to lose all your data. Or am I missing something? (PS, top posting is bad) Tom