From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sm02.isp.telecom.li ([217.173.238.131]:33197 "EHLO sm02.isp.telecom.li" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752483AbaCOLWi (ORCPT ); Sat, 15 Mar 2014 07:22:38 -0400 Received: from [80.248.201.43] (helo=[192.168.1.35]) by sm01.isp.telecom.li with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.77) (envelope-from ) id 1WOmUD-0000uI-6L for fio@vger.kernel.org; Sat, 15 Mar 2014 12:10:42 +0100 Message-ID: <53243539.5010405@adon.li> Date: Sat, 15 Mar 2014 12:10:49 +0100 From: jvogt MIME-Version: 1.0 Subject: correct file size to use Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: fio-owner@vger.kernel.org List-Id: fio@vger.kernel.org To: fio@vger.kernel.org Hi list I was wondering: When i start fio --name=/srv/mail/test --size=10M --direct=1 --runtime=60 --time_based --group_reporting --refill_buffer --rw=read --numjobs=1 I get as result: read : io=1177.4MB, bw=20093KB/s, iops=5023, runt= 60000msec But when I do a fio --name=/srv/mail/test --size=10G --direct=1 --runtime=60 --time_based --group_reporting --refill_buffer --rw=read --numjobs=1 The result is: read : io=976692KB, bw=16278KB/s, iops=4069, runt= 60001msec (decrease of 20%, in some scenarios it's even worse with more than 30%) So how does the file size influence the speed (iops, bandwith)? My understanding was that it is not important from which filesize we are reading from - important is the block size and if the filesize is not big enough, fio just restarts to read the file from the beginning. How can that be explained? And which sizes should be used to get reliable results? Thanks Josef