From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brad Campbell Subject: Re: md raid6: slow resync if fs is mounted rw Date: Wed, 26 Feb 2014 10:31:55 +0800 Message-ID: <530D521B.7060509@fnarfbargle.com> References: <530D1F53.5070703@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <530D1F53.5070703@gmail.com> Sender: linux-raid-owner@vger.kernel.org To: Jakob Unterwurzacher , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 26/02/14 06:55, Jakob Unterwurzacher wrote: > Dear list, > > I am seeing a strange performance issue on a 4 x 4TB md raid6 on kernel > 3.12. Initial resync goes nice and fast at 130MB/s: > >> # cat /proc/mdstat >> Personalities : [raid1] [raid6] [raid5] [raid4] >> md1 : active raid6 sda3[0] sdd3[3] sdc3[2] sdb3[1] >> 7751269376 blocks super 1.2 level 6, 512k chunk, algorithm 2 [4/4] [UUUU] >> [=>...................] resync = 7.5% (293925504/3875634688) finish=458.4min speed=130210K/sec >> >> md0 : active raid1 sda2[0] sdd2[3] sdc2[2] sdb2[1] >> 29280128 blocks super 1.2 [4/4] [UUUU] >> >> unused devices: > > ...unless the ext4 filesystem on the array is mounted read-write! > Then, speed plummets to 1 - 7MB/s. The filesystem is empty and totally > idle; a simple "mount -o remount,ro" restores the speed to 130MB/s. > You are probably expeririencing an effect of this : http://www.thomas-krenn.com/en/wiki/Ext4_Filesystem#Lazy_Initialization Regards, Brad