From owner-freebsd-hackers Mon Nov 24 21:16:47 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id VAA12021 for hackers-outgoing; Mon, 24 Nov 1997 21:16:47 -0800 (PST) (envelope-from owner-freebsd-hackers) Received: from nomis.Simon-Shapiro.ORG (nomis.i-Connect.Net [206.190.143.100]) by hub.freebsd.org (8.8.7/8.8.7) with SMTP id VAA11941 for ; Mon, 24 Nov 1997 21:16:33 -0800 (PST) (envelope-from shimon@nomis.Simon-Shapiro.ORG) Received: (qmail 12398 invoked by uid 1000); 25 Nov 1997 05:13:47 -0000 Message-ID: X-Mailer: XFMail 1.2-beta-111797 [p0] on FreeBSD X-Priority: 3 (Normal) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit MIME-Version: 1.0 In-Reply-To: <199711180932.EAA01115@dyson.iquest.net> Date: Mon, 24 Nov 1997 21:13:47 -0800 (PST) Reply-To: shimon@simon-shapiro.org Organization: Me, Just me... From: Simon Shapiro To: "John S. Dyson" Subject: Re: Optimizing HD I/O. What size to use to read/write? Cc: hackers@FreeBSD.ORG, reyesf@super.zippo.com Sender: owner-freebsd-hackers@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk On 18-Nov-97 John S. Dyson wrote: > Francisco Reyes said: >> I am going to start working on a program which will be heavy on I/O. >> I was wondering what would be a good size to read/write at a time. >> >> What is the minimun block size FreeBSD allocates? 4K? 8K? Is it HD >> dependent? >> > One more comment, if you are doing sequential I/O, you really don't > want > to do read/writes less than 4K-8K. You are likely into diminishing > returns beyond 8K. I'd say it applies to random access even more. Especially if there is more than one client for the disk I/O. On SCSI, up to about 8K, the dominant factor is bus handling, data is a small fraction. After 8K data starts showing up (and this is where wide/ultra/shmultra start making a difference). > > -- > John > dyson@freebsd.org > jdyson@nc.com If Microsoft Built Cars: There would be an "Engine Pro" with bigger turbos, but it would be slower on most existing roads. Sincerely Yours, Simon Shapiro Shimon@Simon-Shapiro.ORG Voice: 503.799.2313