Received: from localhost (unknown [200.46.204.187]) by postgresql.org (Postfix) with ESMTP id 38E7E2E31C2 for ; Wed, 26 Dec 2007 18:11:14 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.187]) (amavisd-maia, port 10024) with ESMTP id 91222-03 for ; Wed, 26 Dec 2007 18:11:03 -0400 (AST) Received: from mx00.pub.collaborativefusion.com (mx00.pub.collaborativefusion.com [206.210.89.199]) by postgresql.org (Postfix) with ESMTP id E06B62E31DB for ; Wed, 26 Dec 2007 18:11:06 -0400 (AST) Received: from vanquish.pitbpa0.priv.collaborativefusion.com (vanquish.pitbpa0.priv.collaborativefusion.com [192.168.2.61]) (SSL: TLSv1/SSLv3,256bits,AES256-SHA) by wingspan with esmtp; Wed, 26 Dec 2007 17:11:05 -0500 id 00056405.4772D179.0001380A Date: Wed, 26 Dec 2007 17:11:05 -0500 From: Bill Moran To: Mark Mielke Cc: david@lang.hm, Florian Weimer , Fernando Hevia , 'pgsql-performance' Subject: Re: With 4 disks should I go for RAID 5 or RAID 10 Message-Id: <20071226171105.889f6146.wmoran@collaborativefusion.com> In-Reply-To: <4772CE34.2040608@mark.mielke.cc> References: <0f8201c847f6$08e15090$8f01010a@iptel.com.ar> <87zlvxnpkl.fsf@mid.deneb.enyo.de> <4772CA58.5050406@mark.mielke.cc> <4772CE34.2040608@mark.mielke.cc> Organization: Collaborative Fusion X-Mailer: Sylpheed 2.4.7 (GTK+ 2.12.1; i386-portbld-freebsd6.2) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200712/386 X-Sequence-Number: 28202 In response to Mark Mielke : > david@lang.hm wrote: > > On Wed, 26 Dec 2007, Mark Mielke wrote: > > > >> Florian Weimer wrote: > >>>> seek/read/calculate/seek/write since the drive moves on after the > >>>> read), when you read you must read _all_ drives in the set to check > >>>> the data integrity. > >>> I don't know of any RAID implementation that performs consistency > >>> checking on each read operation. 8-( > >> Dave had too much egg nog... :-) > >> Yep - checking consistency on read would eliminate the performance > >> benefits of RAID under any redundant configuration. > > except for raid0, raid is primarily a reliability benifit, any > > performance benifit is incidental, not the primary purpose. > > that said, I have heard of raid1 setups where it only reads off of one > > of the drives, but I have not heard of higher raid levels doing so. > What do you mean "heard of"? Which raid system do you know of that reads > all drives for RAID 1? I'm fairly sure that FreeBSD's GEOM does. Of course, it couldn't be doing consistency checking at that point. -- Bill Moran Collaborative Fusion Inc. http://people.collaborativefusion.com/~wmoran/ wmoran@collaborativefusion.com Phone: 412-422-3463x4023