From owner-freebsd-current Sun Oct 6 18:43: 0 2002 Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id D119137B401 for ; Sun, 6 Oct 2002 18:42:58 -0700 (PDT) Received: from wantadilla.lemis.com (wantadilla.lemis.com [192.109.197.80]) by mx1.FreeBSD.org (Postfix) with ESMTP id 58ECA43E7B for ; Sun, 6 Oct 2002 18:42:57 -0700 (PDT) (envelope-from grog@lemis.com) Received: by wantadilla.lemis.com (Postfix, from userid 1004) id 4343E812EA; Mon, 7 Oct 2002 11:12:55 +0930 (CST) Date: Mon, 7 Oct 2002 11:12:55 +0930 From: Greg 'groggy' Lehey To: Matthew Dillon Cc: Vallo Kallaste , Lars Eggert , Poul-Henning Kamp , n0go013 , current Subject: ccd performance (was: [ GEOM tests ] vinum drives lost) Message-ID: <20021007014255.GC93490@wantadilla.lemis.com> References: <62515.1033758160@critter.freebsd.dk> <3D9DEFF7.7050508@isi.edu> <20021005125505.GA1248@tiiu.internal> <20021005221456.GR83766@wantadilla.lemis.com> <20021006072155.GA1117@tiiu.internal> <200210061830.g96IUGNF043142@apollo.backplane.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200210061830.g96IUGNF043142@apollo.backplane.com> User-Agent: Mutt/1.4i Organization: The FreeBSD Project Phone: +61-8-8388-8286 Fax: +61-8-8388-8725 Mobile: +61-418-838-708 WWW-Home-Page: http://www.FreeBSD.org/ X-PGP-Fingerprint: 9A1B 8202 BCCE B846 F92F 09AC 22E6 F290 507A 4223 Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Sunday, 6 October 2002 at 11:30:16 -0700, Matthew Dillon wrote: > Yes, ccd is fairly light weight. 'man tuning' and 'man ccd' has > a lot of information on how to use it. I generally recommend > using a stripe size of 1152 for multitasking loads. Sectors? Why particularly this value? > Only use a small/tiny stripe size if you need single-tasking > sequential performance (and even then you can take tune the > stripe to the drive's own caching capability). > > The biggest mistake most people make when using striping is that > they use too small a stripe size which causes nearly every read() or > write() to have to be split across multiple drives, which multiplies > the overhead, or causes sequential reads of medium sized files to > constantly seek multiple drives, destroying the effectiveness of having > two seekable heads in the first place. Pretty much exactly what I preach. One disadvantage of large stripes is that they require careful coding to optimize. I haven't looked at ccd, but I know a lot of cheap hardware RAID arrays always read an entire stripe at a time, which requires more memory and takes longer. Have you checked ccd for this? Greg -- See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message