From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.fusionio.com ([64.244.102.31]:54309 "EHLO mx2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932084Ab0KMUC7 (ORCPT ); Sat, 13 Nov 2010 15:02:59 -0500 Message-ID: <4CDEEEE5.5060305@fusionio.com> Date: Sat, 13 Nov 2010 21:02:45 +0100 From: Jens Axboe MIME-Version: 1.0 Subject: Re: IOPS higher than expected on randwrite, direct=1 tests References: <20101109182801.GP15588@sebastiankayser.de> <20101110082223.GB14261@sebastiankayser.de> <20101111162222.GO28050@sebastiankayser.de> <20101112134359.GR28050@sebastiankayser.de> In-Reply-To: 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: Shawn Lewis Cc: Sebastian Kayser , fio@vger.kernel.org >> I wonder how many times I saw someone - including myself - fire up >> bonnie++ or iozone with a rather small test file compared to the full >> disk size ... Thanks very much everyone! This was an (overdue) eye >> opener. > In addition, testing with a file is dependent on the state of the file > system. For example, if you're using a 100GB file and there's not enough > contiguous free space to lay it out in one chunk you could have regions on > different parts of the disk. Further, even there is enough space, that space > could be near the inner or outer diameter which would also affect > performance. > > There is a way to get a file address to lba map (which would give you some > insight into how a file is laid out). I think there's a syscall. Jens should > know. Yep, you can use FIBMAP/FIEMAP to walk the extents of the file and get a full map of how it's laid out on disk. Not sure if there are tools that'll do this for you, if not is pretty trivial to write. -- Jens Axboe