From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dkim2.fusionio.com ([66.114.96.54]:44868 "EHLO dkim2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932207Ab3DRV67 (ORCPT ); Thu, 18 Apr 2013 17:58:59 -0400 Received: from mx1.fusionio.com (unknown [10.101.1.160]) by dkim2.fusionio.com (Postfix) with ESMTP id B74759A0420 for ; Thu, 18 Apr 2013 15:58:58 -0600 (MDT) Date: Thu, 18 Apr 2013 17:58:56 -0400 From: Josef Bacik To: Matt Pursley CC: "linux-btrfs@vger.kernel.org" Subject: Re: One random read streaming is fast (~1200MB/s), but two or more are slower (~750MB/s)? Message-ID: <20130418215856.GA2305@localhost.localdomain> References: <20130417065506.GA21083@panda> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" In-Reply-To: Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Wed, Apr 17, 2013 at 07:50:09PM -0600, Matt Pursley wrote: > Hey All, > > Here are the results of making and reading back a 13GB file on > "mdraid6 + ext4", "mdraid6 + btrfs", and "btrfsraid6 + btrfs". > > Seems to show that: > 1) "mdraid6 + ext4" can do ~1100 MB/s for these sequential reads with > either one or two files at once. > 2) "btrfsraid6 + btrfs" can do ~1100 MB/s for sequential reads with > one file at a time, but only ~750 MB/s with two (or more). > 3) "mdraid6 + btrfs" can only do ~750 MB/s for these sequential reads > with either one or two files at once. > > > So, seems like the speed drop is related more to the btrfs files > system, then the experimental raid. > Although it is interesting that btrfs can only do the full ~1100 MB/s > with a single file on the btrfsraid6, but not mdraid6. > > > Anyway, just some more info and reproducible results. > > I have also opened a ticket in bugzilla.kernel.org for this issue here... > https://bugzilla.kernel.org/show_bug.cgi?id=56771 > This is strange, and I can't see any reason why this would happen. I'll try and reproduce next week when I'm back from LSF. Thanks, Josef