Received: from localhost (unknown [200.46.208.211]) by mail.postgresql.org (Postfix) with ESMTP id 21A3D633888 for ; Wed, 1 Apr 2009 19:15:44 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.208.211]) (amavisd-maia, port 10024) with ESMTP id 39370-01 for ; Wed, 1 Apr 2009 19:15:36 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from EXHUB018-2.exch018.msoutlookonline.net (exhub018-2.exch018.msoutlookonline.net [64.78.17.17]) by mail.postgresql.org (Postfix) with ESMTP id 21E2C632F09 for ; Wed, 1 Apr 2009 19:15:42 -0300 (ADT) Received: from EXVMBX018-1.exch018.msoutlookonline.net ([64.78.17.47]) by EXHUB018-2.exch018.msoutlookonline.net ([64.78.17.17]) with mapi; Wed, 1 Apr 2009 15:15:40 -0700 From: Scott Carey To: Scott Marlowe , Stef Telford CC: Greg Smith , Mark Kirkwood , "pgsql-performance@postgresql.org" Date: Wed, 1 Apr 2009 15:15:36 -0700 Subject: Re: Raid 10 chunksize Thread-Topic: [PERFORM] Raid 10 chunksize Thread-Index: Acmy6pqQht9xpYMjQ9epljRke21g8QALMcLR Message-ID: In-Reply-To: Accept-Language: en-US Content-Language: en X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0 tagged_above=0 required=5 tests=AWL=0.000 X-Spam-Level: X-Archive-Number: 200904/33 X-Sequence-Number: 33400 On 4/1/09 9:54 AM, "Scott Marlowe" wrote: > On Wed, Apr 1, 2009 at 10:48 AM, Stef Telford wrote: >> Scott Marlowe wrote: >>> On Wed, Apr 1, 2009 at 10:15 AM, Stef Telford wrote: >>>=20 >>>> =A0 =A0 I do agree that the benefit is probably from write-caching, bu= t I >>>> think that this is a 'win' as long as you have a UPS or BBU adaptor, >>>> and really, in a prod environment, not having a UPS is .. well. Crazy = ? >>>>=20 >>>=20 >>> You do know that UPSes can fail, right? =A0En masse sometimes even. >>>=20 >> Hello Scott, >> =A0 =A0Well, the only time the UPS has failed in my memory, was during t= he >> great Eastern Seaboard power outage of 2003. Lots of fond memories >> running around Toronto with a gas can looking for oil for generator >> power. This said though, anything could happen, the co-lo could be taken >> out by a meteor and then sync on or off makes no difference. >=20 > Meteor strike is far less likely than a power surge taking out a UPS. > I saw a whole data center go black when a power conditioner blew out, > taking out the other three power conditioners, both industrial UPSes > and the switch for the diesel generator. And I have friends who have > seen the same type of thing before as well. The data is the most > expensive part of any server. >=20 Yeah, well I=B9ve had a RAID card die, which broke its Battery backed cache= . They=B9re all unsafe, technically. In fact, not only are battery backed caches unsafe, but hard drives. They can return bad data. So if you want to be really safe: 1: don't use Linux -- you have to use something with full data and metadata checksums like ZFS or very expensive proprietary file systems. 2: combine it with mirrored SSD's that don't use write cache (so you can have fsync perf about as good as a battery backed raid card without that risk). 4: keep a live redundant system with a PITR backup at another site that can recover in a short period of time. 3: Run in a datacenter well underground with a plutonium nuclear power supply. Meteor strikes and Nuclear holocaust, beware!