From owner-freebsd-questions@FreeBSD.ORG Thu Jan 25 22:26:55 2007 Return-Path: X-Original-To: freebsd-questions@freebsd.org Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 8147C16A401 for ; Thu, 25 Jan 2007 22:26:55 +0000 (UTC) (envelope-from freebsd-questions@m.gmane.org) Received: from ciao.gmane.org (main.gmane.org [80.91.229.2]) by mx1.freebsd.org (Postfix) with ESMTP id 0790A13C45D for ; Thu, 25 Jan 2007 22:26:54 +0000 (UTC) (envelope-from freebsd-questions@m.gmane.org) Received: from list by ciao.gmane.org with local (Exim 4.43) id 1HAD3N-0004xM-9q for freebsd-questions@freebsd.org; Thu, 25 Jan 2007 23:26:45 +0100 Received: from 89-172-36-253.adsl.net.t-com.hr ([89.172.36.253]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 25 Jan 2007 23:26:45 +0100 Received: from ivoras by 89-172-36-253.adsl.net.t-com.hr with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 25 Jan 2007 23:26:45 +0100 X-Injected-Via-Gmane: http://gmane.org/ To: freebsd-questions@freebsd.org From: Ivan Voras Date: Thu, 25 Jan 2007 23:26:37 +0100 Lines: 57 Message-ID: References: <25E0702D-C3A3-4B6B-BC56-D1BC5C1347F5@cyberlifelabs.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigBFCCE686D297BCA4D8A66E33" X-Complaints-To: usenet@sea.gmane.org X-Gmane-NNTP-Posting-Host: 89-172-36-253.adsl.net.t-com.hr User-Agent: Thunderbird 1.5.0.9 (Windows/20061207) In-Reply-To: <25E0702D-C3A3-4B6B-BC56-D1BC5C1347F5@cyberlifelabs.com> X-Enigmail-Version: 0.94.1.2 Sender: news Subject: Re: RAID Performance Questions X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 25 Jan 2007 22:26:55 -0000 This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigBFCCE686D297BCA4D8A66E33 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Milo Hyson wrote: > I also ran some performance tests with a stock build of PostgreSQL 8.0 > to get a different angle on things. Two tests were run on each of the > UDMA system drive, the RAID 5 unit, and the RAID 10 unit. The first > tested sequential-scans through a 58,000+ record table. The second > tested random index-scans of the same table. These were read-only tests= > -- no write tests were performed. The results are as follows: >=20 > Unit Seq/sec Index/sec > ------------------------------ > single 0.550 2048.983 > raid5 0.533 2063.900 > raid10 0.533 2093.283 58,000 records is WAY too small for any benefits to come out, unless the records are very large ("wide"). The database and the OS will cache as much data they can - with such a small number of records it's very probable they will all be cached and the drives won't get any IO (and it's lucky for you that it works this way). You can verify this hypothesis with iostat and similar utilities. This is also something you'll need to consider: unless you have more data than fits in your memory, don't bother with the drives. When your data DOES grow enough that it doesn't fit in memory (or actually - not all of it, just the mostly accessed bits), you'll take a dramatic performance hit which you can fix only with a large numbers of drives (as other said - no less than 5 fast drives to get any kind of decent performance). In that case, it's way cheaper and faster to add as much memory as the motherboard can handle before even touching the drives. (the above explanation holds for read-mostly loads. for write intensive loads, go immediately to the 5+ drives option and try to avoid RAID5). --------------enigBFCCE686D297BCA4D8A66E33 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.4 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFFuS6dldnAQVacBcgRAj5wAJ9MX7tbmjKtrSJAL+gVsbctju2nFACcDPIU ohuRvaHi9jSk/GtWX4x0OtY= =GtJq -----END PGP SIGNATURE----- --------------enigBFCCE686D297BCA4D8A66E33--