From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.virtall.com ([178.63.195.102]:55849 "EHLO mail.virtall.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751953AbcEOKoO (ORCPT ); Sun, 15 May 2016 06:44:14 -0400 Received: from localhost (localhost [127.0.0.1]) by mailext.virtall.com (Postfix) with ESMTP id 278E134E893 for ; Sun, 15 May 2016 12:24:48 +0200 (CEST) Received: from mailext.virtall.com ([127.0.0.1]) by localhost (web1.virtall.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id vC1E1f5a0mWN for ; Sun, 15 May 2016 12:24:47 +0200 (CEST) Received: from admin.virtall.com (localhost [127.0.0.1]) by mailext.virtall.com (Postfix) with ESMTP for ; Sun, 15 May 2016 12:24:47 +0200 (CEST) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Date: Sun, 15 May 2016 19:24:47 +0900 From: Tomasz Chmielewski To: linux-btrfs Subject: btrfs RAID-1 vs md RAID-1? Message-ID: <83719f27dd5cdc406fd3fd24e7b82a9f@admin.virtall.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: I'm trying to read two large files in parallel from a 2-disk RAID-1 btrfs setup (using kernel 4.5.3). According to iostat, one of the disks is 100% saturated, while the other disk is around 0% busy. Is it expected? With two readers from the same disk, each file is being read with ~50 MB/s from disk (with just one reader from disk, the speed goes up to around ~150 MB/s). In md RAID, with many readers, it will try to distribute the reads - after md manual on http://linux.die.net/man/4/md: Raid1 (...) Data is read from any one device. The driver attempts to distribute read requests across all devices to maximise performance. Raid5 (...) This also allows more parallelism when reading, as read requests are distributed over all the devices in the array instead of all but one. Are there any plans to improve this is btrfs? Tomasz Chmielewski http://wpkg.org