Received: from localhost (unknown [200.46.204.182]) by postgresql.org (Postfix) with ESMTP id 4D5219FA64B for ; Fri, 7 Sep 2007 05:15:21 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.182]) (amavisd-maia, port 10024) with ESMTP id 57208-06 for ; Fri, 7 Sep 2007 05:14:56 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.5 Received: from mx01.bfk.de (mx01.bfk.de [193.227.124.2]) by postgresql.org (Postfix) with ESMTP id A55129FA586 for ; Fri, 7 Sep 2007 05:15:15 -0300 (ADT) Received: from mx00.int.bfk.de ([10.119.110.2]) by mx01.bfk.de with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) id 1ITYzg-0002yQ-LM; Fri, 07 Sep 2007 10:15:12 +0200 Received: from fweimer by bfk.de with local id 1ITYzK-00042h-JE; Fri, 07 Sep 2007 10:14:50 +0200 To: Arjen van der Meijden Cc: Scott Marlowe , Harsh Azad , pgsql-performance@postgresql.org Subject: Re: SAN vs Internal Disks References: <46E0571A.7000102@tweakers.net> From: Florian Weimer Date: Fri, 07 Sep 2007 10:14:50 +0200 In-Reply-To: <46E0571A.7000102@tweakers.net> (Arjen van der Meijden's message of "Thu, 06 Sep 2007 21:38:02 +0200") Message-ID: <82myvynb7p.fsf@mid.bfk.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200709/112 X-Sequence-Number: 26657 * Arjen van der Meijden: > The disadvantage of using Areca or 3Ware is obviously the lack of > support in A-brand servers and the lack of support for SAS-disks. Only > recently Areca has stepped in the SAS-market, but I have no idea how > easily those controllers are integrated in standard servers (they tend > to be quite large, which will not fit in 2U and maybe not even in 3U > or 4U-servers). Recent 3ware controllers are a bit on the hot side, too. We had to switch from two 12 port controllers to a single 24 port controller because of that (combined with an unlucky board layout: the two 8x PCIe connectors are next to each other). Unfortunately, read performance maxes out at about 8 disks in a RAID-10 configuration. Software RAID-0 across hardware RAID-1 is significantly faster (factor of 3 to 5 in low-level benchmarks). However, it seems that something in this stack does not enforce write barriers properly, so I don't think we will use this in production. RAID-6 doesn't perform well, either (especially for several processes reading different files sequentially). We'll probably split the 24 disks into a couple of RAID-10s, and distribute tables and indexes manually among the file systems. This is a bit disappointing, especially because the system is able to read at 800+ MB/s, as shown by the software-RAID-on-hardware-RAID configuration. I haven't seen 24-disk benchmarks with Areca controllers. A comparison might be interesting. --=20 Florian Weimer BFK edv-consulting GmbH http://www.bfk.de/ Kriegsstra=DFe 100 tel: +49-721-96201-1 D-76133 Karlsruhe fax: +49-721-96201-99