X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by postgresql.org (Postfix) with ESMTP id EECFA9DC9B6 for ; Sat, 24 Dec 2005 18:37:00 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 50247-07 for ; Sat, 24 Dec 2005 18:37:02 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey- Received: from floppy.pyrenet.fr (floppy.pyrenet.fr [194.116.145.2]) by postgresql.org (Postfix) with ESMTP id 456999DC821 for ; Sat, 24 Dec 2005 18:36:58 -0400 (AST) Received: by floppy.pyrenet.fr (Postfix, from userid 106) id 9720F33A69; Sat, 24 Dec 2005 23:37:00 +0100 (MET) From: William Yu X-Newsgroups: pgsql.performance Subject: Re: What's the best hardver for PostgreSQL 8.1? Date: Sat, 24 Dec 2005 14:36:57 -0800 Organization: Hub.Org Networking Services Lines: 14 Message-ID: References: <43A84D03.7090002@ritek.hu> <200512212209.50234.caseroj@comcast.net> <200512212231.55100.caseroj@comcast.net> <20051224135042.484c6e32.frank@wiles.org> <6.2.5.6.0.20051224161551.01dc5d98@earthlink.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@news.hub.org User-Agent: Mozilla Thunderbird 1.0.7 (X11/20050923) X-Accept-Language: en-us, en In-Reply-To: To: pgsql-performance@postgresql.org X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.03 required=5 tests=[AWL=0.030] X-Spam-Score: 0.03 X-Spam-Level: X-Archive-Number: 200512/600 X-Sequence-Number: 16421 David Lang wrote: > raid 5 is bad for random writes as you state, but how does it do for > sequential writes (for example data mining where you do a large import > at one time, but seldom do other updates). I'm assuming a controller > with a reasonable amount of battery-backed cache. Random write performance (small block that only writes to 1 drive): 1 write requires N-1 reads + N writes --> 1/2N-1 % Sequential write performance (write big enough block to use all N drives): N-1 Write requires N writes --> N-1/N % Assuming enough cache so all reads/writes are done in 1 transaction + onboard processor calcs RAID parity fast enough to not cause an extra delay.