From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from plane.gmane.org ([80.91.229.3]:37635 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752286Ab3LMLJI (ORCPT ); Fri, 13 Dec 2013 06:09:08 -0500 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1VrQcF-0001qo-54 for linux-btrfs@vger.kernel.org; Fri, 13 Dec 2013 12:09:07 +0100 Received: from cpc21-stap10-2-0-cust974.12-2.cable.virginm.net ([86.0.163.207]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Fri, 13 Dec 2013 12:09:07 +0100 Received: from m_btrfs by cpc21-stap10-2-0-cust974.12-2.cable.virginm.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Fri, 13 Dec 2013 12:09:07 +0100 To: linux-btrfs@vger.kernel.org From: Martin Subject: Re: btrfs raid multiple devices IO utilisation Date: Fri, 13 Dec 2013 11:08:56 +0000 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 In-Reply-To: Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 13/12/13 09:13, Duncan wrote: > Martin posted on Thu, 12 Dec 2013 13:39:00 +0000 as excerpted: > >> Some time back, I noticed that with a two HDD btrfs raid1, some tasks >> suffered ALL the IO getting choked onto just one HDD! >> >> That turned out to be a feature of the btrfs code whereby a device is >> chosen depending on the process ID. For some cases such as in a bash >> loop, the PID increments by two for each iteration and so only one HDD >> ever gets hit... > > Unfortunately, yes... > ... Of course that's if the queue > length is reasonably accessible to btrfs, as you already asked in the bit > I snipped as out of my knowledgeable reply range. And that's the bit that is outside of my knowledge... Hence the question. Here's hoping someone can give a pointer before I need to delve into other code such as for 'atop' to see how it is done there if I'm to take a stab at it. Or if someone is already coding something up, please let us know? Or: >>From within btrfs code, is there an easy/fast/any way to check the IO queue length for whatever btrfs target device? Regards, Martin