From owner-freebsd-hardware@FreeBSD.ORG Tue Dec 25 03:45:55 2007 Return-Path: Delivered-To: freebsd-hardware@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 968C316A417; Tue, 25 Dec 2007 03:45:55 +0000 (UTC) (envelope-from bsd@fluffles.net) Received: from mail.fluffles.net (fluffles.net [80.69.95.190]) by mx1.freebsd.org (Postfix) with ESMTP id 604D313C458; Tue, 25 Dec 2007 03:45:55 +0000 (UTC) (envelope-from bsd@fluffles.net) Received: from [10.0.0.18] (82-169-78-205.dsl.ip.tiscali.nl [82.169.78.205]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: info@fluffles.net) by mail.fluffles.net (Postfix) with ESMTP id ECCC5B2A1F1; Tue, 25 Dec 2007 04:25:30 +0100 (CET) Message-ID: <47707966.4030309@fluffles.net> Date: Tue, 25 Dec 2007 04:30:46 +0100 From: "fluffles.net" User-Agent: Thunderbird 2.0.0.6 (X11/20071022) MIME-Version: 1.0 To: Ivan Voras References: <475D7866.1070803@hangwithme.com> <475D7D60.4040701@fuckner.net> <20071212003235.G54053@3jane.math.ualberta.ca> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: freebsd-fs@freebsd.org, freebsd-hardware@freebsd.org Subject: Re: large disk > 8 TB X-BeenThere: freebsd-hardware@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: General discussion of FreeBSD hardware List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 25 Dec 2007 03:45:55 -0000 Ivan Voras wrote: > Barkley Vowk wrote: > > >> It looks like he created a 32bit disk label. He needs to use either the >> raw device, or gpt partitions I think. >> >> Ie. /dev/mdid1 or /dev/mdid1p1 instead of /dev/mdid1s1 >> > > You're right :) > I didn't think of checking that - a wrong assumption at my part. > If you are using partitions on a RAID device, you have to make sure you don't end up with a stripe misalignment. If there is misalignment then you end up requiring 2 I/O requests whereas otherwise 1 I/O request would suffice. Naturally this decreases IO performance (less IOps). To avoid a misalignment you have two options: - not using partitions, but using the raw device like Barkley said - use partitions (GPT or normal) and create one large partition, which starts at offset 1MiB (not MB!) thus 1024*1024 bytes. Note that you probably need to convert this to sectors (512 bytes). If you do option 2 right, then the partition will start at precisely the start of a new stripe block - thus there is no misalignment. You can use offsets like 64KiB and 128KiB but i prefer to use 1MiB since that will work with all stripesizes (up to 1MiB, which is rarely used). Merry christmas to all. :) Regards, Veronica