From owner-freebsd-current@FreeBSD.ORG Mon Mar 31 20:32:51 2008 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 503F21065676; Mon, 31 Mar 2008 20:32:51 +0000 (UTC) (envelope-from scottl@samsco.org) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.freebsd.org (Postfix) with ESMTP id 08F878FC17; Mon, 31 Mar 2008 20:32:50 +0000 (UTC) (envelope-from scottl@samsco.org) Received: from phobos.samsco.home (phobos.samsco.home [192.168.254.11]) (authenticated bits=0) by pooker.samsco.org (8.13.8/8.13.8) with ESMTP id m2VKLiOb064468; Mon, 31 Mar 2008 14:21:44 -0600 (MDT) (envelope-from scottl@samsco.org) Message-ID: <47F147D8.3030905@samsco.org> Date: Mon, 31 Mar 2008 14:21:44 -0600 From: Scott Long User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:1.8.1.11) Gecko/20071128 SeaMonkey/1.1.7 MIME-Version: 1.0 To: Ivan Voras References: In-Reply-To: X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-1.4 required=5.4 tests=ALL_TRUSTED autolearn=failed version=3.1.8 X-Spam-Checker-Version: SpamAssassin 3.1.8 (2007-02-13) on pooker.samsco.org Cc: freebsd-current@freebsd.org Subject: Re: Are large RAID stripe sizes useful with FreeBSD? X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 31 Mar 2008 20:32:51 -0000 Ivan Voras wrote: > Most of new hardware RAID controllers offer stripe sizes of 128K, 256K > and some also have 512K and 1M stripes. In the simplest case of RAID0 of > two drives, knowing that the data is striped across the drives and that > FreeBSD issues IO request of at most 64K, is it useful to set stripe > sizes to anything larger than 32K? I suppose something like TCQ would > help the situation but does anyone know how is this situation usually > handled on the RAID controllers? Large I/O sizes and large stripe sizes only benefit benchmarks and a narrow class of real-world applications. Large stripes have the potential to actually hurt RAID-5 performance since they make it much harder for the card to a full stripe replacement instead of a read-modify-xor-write. I hate to be all preachy and linux-like and tell you want you need or don't need, but in all honesty, large i/o's and stripes usually don't help typical filesystem-based mail/squid/mysql/apache server apps. I do have proof-of-concept patches to allow larger I/O's for selected controllers on 64-bit FreeBSD platforms, and I intend to clean up and commit those patches in the next few weeks (no, I'm not ready for nor looking for testers at this time, sorry). Scott