From owner-freebsd-hackers@FreeBSD.ORG Fri Jan 9 16:50:21 2009 Return-Path: Delivered-To: hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B0490106566B for ; Fri, 9 Jan 2009 16:50:21 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from harmony.bsdimp.com (bsdimp.com [199.45.160.85]) by mx1.freebsd.org (Postfix) with ESMTP id 5BB6D8FC1E for ; Fri, 9 Jan 2009 16:50:21 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from localhost (localhost [127.0.0.1]) by harmony.bsdimp.com (8.14.2/8.14.1) with ESMTP id n09GoBDW000681 for ; Fri, 9 Jan 2009 09:50:11 -0700 (MST) (envelope-from imp@bsdimp.com) Date: Fri, 09 Jan 2009 09:50:27 -0700 (MST) Message-Id: <20090109.095027.-1672857892.imp@bsdimp.com> To: hackers@freebsd.org From: "M. Warner Losh" X-Mailer: Mew version 5.2 on Emacs 21.3 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Subject: 3x read to write ratio on dump/restore X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 09 Jan 2009 16:50:21 -0000 I just copied a disk using dump + restore. I noticed something through the whole run of this 500GB operation: L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name 3 231 231 14754 9.5 0 0 0.0 97.5| da1s1a 0 39 0 0 0.0 39 4982 10.0 38.7| da2s1a The read kBps was 3x the write kBps. While the dump is going through the raw device, and the restore is going through the file system, I can't imagine why we'd have such a huge difference that would be utter consistent for the whole 15 hour run. Any ideas what gives? I observed this with 16MB cache and with 32MB cache, fwiw. Warner