From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from 87-104-106-3-dynamic-customer.profibernet.dk ([87.104.106.3]:39793 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755705Ab1HaVib (ORCPT ); Wed, 31 Aug 2011 17:38:31 -0400 Message-ID: <4E5EA9D0.10109@kernel.dk> Date: Wed, 31 Aug 2011 15:38:24 -0600 From: Jens Axboe MIME-Version: 1.0 Subject: Re: fio file test patterns References: <4E5E91D9.4000702@fusionio.com> <4E5EA5DF.5040609@fusionio.com> In-Reply-To: <4E5EA5DF.5040609@fusionio.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: fio-owner@vger.kernel.org List-Id: fio@vger.kernel.org To: Brian Fallik Cc: Jeff Moyer , "fio@vger.kernel.org" On 2011-08-31 15:21, Jens Axboe wrote: >> I also have another (maybe related?) question. Apologies if this >> belongs in a separate thread, but are there any notes explaining why >> fio lays out the files before starting sequential writes? The >> workload I was hoping to simulate is sustained, sequential writes to >> disk. I'm trying to answer the question "How many simultaneous >> 200kBps writers can we support?" Using my current jobs file, fio >> starts by creating the files (e.g "foo0: Laying out IO file(s) (1 >> file(s) / 4MB)") before it starts processing. However, creating the >> files in advance accounts for a chunk of performance that doesn't seem >> to be measured by fio. Am I misunderstanding how to configure fio or >> its intended usage? > > You should be able to set overwrite=0 to avoid that. Are they random > writes? overwrite=0 is even default. I'm thinking the "Laying out IO file" message is confusing, it wont actually write contents first unless you ask it to (with eg overwrite=1). -- Jens Axboe