From owner-freebsd-questions Tue Feb 25 15:31:28 2003 Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 9148F37B401 for ; Tue, 25 Feb 2003 15:31:27 -0800 (PST) Received: from mail.inka.de (quechua.inka.de [193.197.184.2]) by mx1.FreeBSD.org (Postfix) with ESMTP id 5841343FAF for ; Tue, 25 Feb 2003 15:31:26 -0800 (PST) (envelope-from mailnull@mips.inka.de) Received: from kemoauc.mips.inka.de (uucp@) by mail.inka.de with gbsmtp id 18noXk-0002CL-00; Wed, 26 Feb 2003 00:31:24 +0100 Received: from kemoauc.mips.inka.de (localhost [127.0.0.1]) by kemoauc.mips.inka.de (8.12.7/8.12.6) with ESMTP id h1PMTL1s024015 for ; Tue, 25 Feb 2003 23:29:21 +0100 (CET) (envelope-from mailnull@localhost.mips.inka.de) Received: (from mailnull@localhost) by kemoauc.mips.inka.de (8.12.7/8.12.7/Submit) id h1PMTLvA024014 for freebsd-questions@freebsd.org; Tue, 25 Feb 2003 23:29:21 +0100 (CET) From: naddy@mips.inka.de (Christian Weisgerber) Subject: dump: skewed I/O, why? Date: Tue, 25 Feb 2003 22:29:17 +0000 (UTC) Message-ID: Originator: naddy@mips.inka.de (Christian Weisgerber) To: freebsd-questions@freebsd.org Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG During a dump(8) of a filesystem on da0 to a holding file on da1, with nothing else going on, iostat(8) reports figures such as these: da0 da1 cd0 cd1 KB/t tps MB/s KB/t tps MB/s KB/t tps MB/s KB/t tps MB/s 64.00 148 9.28 64.00 24 1.52 0.00 0 0.00 0.00 0 0.00 64.00 134 8.38 64.00 17 1.07 0.00 0 0.00 0.00 0 0.00 63.63 134 8.32 64.00 18 1.10 0.00 0 0.00 0.00 0 0.00 64.00 143 8.96 60.30 24 1.41 0.00 0 0.00 0.00 0 0.00 64.00 140 8.73 63.85 21 1.33 0.00 0 0.00 0.00 0 0.00 64.00 130 8.14 62.13 15 0.93 0.00 0 0.00 0.00 0 0.00 64.00 138 8.63 64.00 18 1.10 0.00 0 0.00 0.00 0 0.00 63.79 137 8.56 64.00 18 1.10 0.00 0 0.00 0.00 0 0.00 63.82 140 8.74 64.00 18 1.10 0.00 0 0.00 0.00 0 0.00 64.00 138 8.61 61.67 24 1.47 0.00 0 0.00 0.00 0 0.00 Why is the I/O ratio so skewed towards reading? I would have expected the I/O on the reading side to mostly match the writing side. Instead, several times as much data appears to be read as is written. And yes, this uses dump's recently introduced -C cache option. -- Christian "naddy" Weisgerber naddy@mips.inka.de To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message