From mboxrd@z Thu Jan 1 00:00:00 1970 From: Justin Piszcz Subject: Linux MD Raid Bug(?) w/Kernel sync_speed_min Option Date: Tue, 8 May 2007 08:27:35 -0400 (EDT) Message-ID: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Kernel: 2.6.21.1 Here is the bug: md2: RAID1 (works fine) md3: RAID5 (only syncs at the sync_speed_min set by the kernel) If I do not run this command: echo 55000 > /sys/block/md3/md/sync_speed_min I will get 2 megabytes per second check speed for RAID 5. However, the odd part is I can leave it the default for RAID1 and it will use the maximum IO available between both drives to run the check. I think there is some kind of bug, essentially with RAID5 check's-- it only runs at the minimum value set (default in the kernel for raid5 is ~2mb/s). md2 : active raid1 sdb3[1] sda3[0] 55681216 blocks [2/2] [UU] [===========>.........] check = 59.1% (32937536/55681216) finish=7.4min speed=50947K/sec md3 : active raid5 sdl1[9] sdk1[8] sdj1[7] sdi1[6] sdh1[5] sdg1[4] sdf1[3] sde1[ 2] sdd1[1] sdc1[0] 1318686336 blocks level 5, 128k chunk, algorithm 2 [10/10] [UUUUUUUUUU] [====>................] check = 24.2% (35578816/146520704) finish=33.3min speed=55464K/sec Set to default kernel settings, either 2000 or 2100: echo 2000 > /sys/block/md3/md/sync_speed_min Then, md3 : active raid5 sdl1[9] sdk1[8] sdj1[7] sdi1[6] sdh1[5] sdg1[4] sdf1[3] sde1[ 2] sdd1[1] sdc1[0] 1318686336 blocks level 5, 128k chunk, algorithm 2 [10/10] [UUUUUUUUUU] [======>..............] check = 31.5% (46191744/146520704) finish=715.7min speed=2335K/sec There is some kind of nasty bug going on here with RAID 5 devices in the kernel. Also, incase you wondered, there is little to no I/O on the RAID 5 device when this check is being run, same for the root volume. Justin.