On Thu, 11 Feb 2010 12:02:56 +0000 Benjamin ESTRABAUD <be@xxxxxxxxxx> wrote: > Hi everybody, > > I am getting a weird issue when I am writing values to > "/sys/block/mdX/md/sync_action". > For instance, I would like to pause a resync or/and a recovery when they > are happening. > I create a RAID 5 as follow: > > mdadm --create -vvv --force --run --metadata=1.2 /dev/md/d0 --level=5 > --size=9429760 --chunk=64 --name=1056856 -n5 --bitmap=internal > --bitmap-chunk=4096 --layout=ls /dev/sde2 /dev/sdb2 /dev/sdc2 /dev/sdf2 > /dev/sdd2 > > The RAID is resyncing: > > # cat /proc/mdstat > Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] > md_d0 : active raid5 sdd2[4] sdf2[3] sdc2[2] sdb2[1] sde2[0] > 37719040 blocks super 1.2 level 5, 64k chunk, algorithm 2 [5/5] > [UUUUU] > [====>................] resync = 22.2% (2101824/9429760) > finish=2.6min speed=46186K/sec > bitmap: 1/1 pages [64KB], 4096KB chunk > > unused devices: <none> > > I then decide to pause its resync: > > # echo idle > /sys/block/md_d0/md/sync_action > > The RAID resync should have paused by now, let's check the sys properties: > > # cat /sys/block/md_d0/md/sync_action > resync > > The resync seems to have not stopped/restarted, let's check dmesg: > > [157287.049715] raid5: raid level 5 set md_d0 active with 5 out of 5 > devices, algorithm 2 > [157287.057601] RAID5 conf printout: > [157287.060909] --- rd:5 wd:5 > [157287.063700] disk 0, o:1, dev:sde2 > [157287.067182] disk 1, o:1, dev:sdb2 > [157287.070664] disk 2, o:1, dev:sdc2 > [157287.074147] disk 3, o:1, dev:sdf2 > [157287.077628] disk 4, o:1, dev:sdd2 > [157287.086813] md_d0: bitmap initialized from disk: read 1/1 pages, set > 2303 bits > [157287.094134] created bitmap (1 pages) for device md_d0 > [157287.113475] md: resync of RAID array md_d0 > [157287.117650] md: minimum _guaranteed_ speed: 1000 KB/sec/disk. > [157287.123555] md: using maximum available idle IO bandwidth (but not > more than 200000 KB/sec) for resync. > [157287.133011] md: using 2048k window, over a total of 9429760 blocks. > [157345.158535] md: md_do_sync() got signal ... exiting > [157345.166057] md: checkpointing resync of md_d0. > [157345.179819] md: resync of RAID array md_d0 > [157345.183993] md: minimum _guaranteed_ speed: 1000 KB/sec/disk. > [157345.189899] md: using maximum available idle IO bandwidth (but not > more than 200000 KB/sec) for resync. > [157345.199353] md: using 2048k window, over a total of 9429760 blocks. > > The resync seem to stop at some stage since: > > [157345.158535] md: md_do_sync() got signal ... exiting > > But it seems to be restarting right after this: > > [157345.179819] md: resync of RAID array md_d0 > > I read in the md.txt documentation that pausing a resync could sometimes > not work if a n event or trigger was triggering it to automatically > restart. However, I don't think I have any trigger that would cause it > to restart. > it then builds perfectly fine. > > I now want to check if the same issue occurs while recovering, after > all, I especially want to be able to pause a recovery, while I don't > really need to pause/restart resyncs. > > Let's say I pull a disk from the bay, fail it and remove it as follow: > > # mdadm --fail /dev/md/d0 /dev/sde2 > mdadm: set /dev/sde2 faulty in /dev/md/d0 > > # mdadm --remove /dev/md/d0 /dev/sde2 > mdadm: hot removed /dev/sde2 > > Now let's add a spare: > > # /opt/soma/bin/mdadm/mdadm --add /dev/md/d0 /dev/sda2 > raid manager: added /dev/sda2 > > The RAID is now recovering: > > # cat /proc/mdstat > Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] > md_d0 : active raid5 sda2[5] sdd2[4] sdf2[3] sdc2[2] sdb2[1] > 37719040 blocks super 1.2 level 5, 64k chunk, algorithm 2 [5/4] > [_UUUU] > [>....................] recovery = 1.7% (169792/9429760) > finish=0.9min speed=169792K/sec > bitmap: 0/1 pages [0KB], 4096KB chunk > > unused devices: <none> > > # cat /sys/block/md_d0/md/sync_action > recover > > Let's try and stop this recovery: > > # echo idle > /sys/block/md_d0/md/sync_action > > [157641.618291] disk 3, o:1, dev:sdf2 > [157641.621774] disk 4, o:1, dev:sdd2 > [157641.632057] md: recovery of RAID array md_d0 > [157641.636413] md: minimum _guaranteed_ speed: 1000 KB/sec/disk. > [157641.642314] md: using maximum available idle IO bandwidth (but not > more than 200000 KB/sec) for recovery. > [157641.651940] md: using 2048k window, over a total of 9429760 blocks. > [157657.120722] md: md_do_sync() got signal ... exiting > [157657.267055] RAID5 conf printout: > [157657.270381] --- rd:5 wd:4 > [157657.273171] disk 0, o:1, dev:sda2 > [157657.276650] disk 1, o:1, dev:sdb2 > [157657.280129] disk 2, o:1, dev:sdc2 > [157657.283605] disk 3, o:1, dev:sdf2 > [157657.287087] disk 4, o:1, dev:sdd2 > [157657.290568] RAID5 conf printout: > [157657.293876] --- rd:5 wd:4 > [157657.296660] disk 0, o:1, dev:sda2 > [157657.300139] disk 1, o:1, dev:sdb2 > [157657.303615] disk 2, o:1, dev:sdc2 > [157657.307096] disk 3, o:1, dev:sdf2 > [157657.310579] disk 4, o:1, dev:sdd2 > [157657.320835] md: recovery of RAID array md_d0 > [157657.325194] md: minimum _guaranteed_ speed: 1000 KB/sec/disk. > [157657.331091] md: using maximum available idle IO bandwidth (but not > more than 200000 KB/sec) for recovery. > [157657.340713] md: using 2048k window, over a total of 9429760 blocks. > [157657.347047] md: resuming recovery of md_d0 from checkpoint. > > I am getting the same issue, the recovery stops, but restarts 200 > milliseconds later. So clearly the resync is pausing - for 200milliseconds.... 'idle' is only really useful to top a 'check' or 'repair'. A 'sync' or 'recovery' md really wants to do, so whenever it seems to be needed it, it does it. What you want is "frozen" which is only available since 2.6.31. > > This clearly indicates that some sort of trigger is automatically > restarting the resync and recovery, but I have no clue as of what could > it be. > > Would anyone here had a similar experience with trying to stop resyncs? > Is there a "magic" variable that would enable or disable automatic > restart of resync/recoveries? > > Would anyone know of a standard event or trigger that would cause a > resync or recovery to automatically restart? > > Thank you very much in advance for your help. > > My Kernel version is: > > 2.6.26.3 > So with that kernel, you cannot freeze a recovery. Why do you want to? A possible option is the mark the array read-only "mdadm --read-only /dev/mdXX". This doesn't work if the array is mounted, but does stop any recovery from happening. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
