From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from plane.gmane.org ([80.91.229.3]:37089 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751895AbcEOXai (ORCPT ); Sun, 15 May 2016 19:30:38 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1b25UP-0001v3-7v for linux-btrfs@vger.kernel.org; Mon, 16 May 2016 01:30:25 +0200 Received: from ip5f5ae06c.dynamic.kabel-deutschland.de ([95.90.224.108]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 16 May 2016 01:30:25 +0200 Received: from hurikhan77 by ip5f5ae06c.dynamic.kabel-deutschland.de with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 16 May 2016 01:30:25 +0200 To: linux-btrfs@vger.kernel.org From: Kai Krakow Subject: Re: btrfs RAID-1 vs md RAID-1? Date: Mon, 16 May 2016 01:29:59 +0200 Message-ID: <20160516012959.2768c42c@jupiter.sol.kaishome.de> References: <83719f27dd5cdc406fd3fd24e7b82a9f@admin.virtall.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-btrfs-owner@vger.kernel.org List-ID: Am Sun, 15 May 2016 19:24:47 +0900 schrieb Tomasz Chmielewski : > 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 Here is an idea that could need improvement: http://permalink.gmane.org/gmane.comp.file-systems.btrfs/17985 -- Regards, Kai Replies to list-only preferred.