On Sat, 3 Dec 2011 12:23:37 +0100 Vincent Pelletier <plr.vincent@xxxxxxxxx> wrote: > Hi. > > Short system description: > up-to-date Debian sid, used on a NAS-ish machine (iscsi with > open-iscsi's kernel module, nfs, dnsmask for netboot), ext4 FS over > RAID1 on both system partition and exported data partitions. > > I would like disks containing raid arrays to spin down, but there are > periodic disk writes which prevent this. > They do not show up in iotop (although it does show a write activity > in the topmost line). > Enabling /proc/sys/vm/block_dump generates the following output: > > <7>[ 918.078079] md0_raid1(304): WRITE block 8 on sda1 (2 sectors) > <7>[ 918.078169] md0_raid1(304): WRITE block 8 on sdc1 (2 sectors) > <7>[ 918.092124] md1_raid1(311): WRITE block 8 on sda5 (2 sectors) > <7>[ 918.092184] md1_raid1(311): WRITE block 8 on sdc5 (2 sectors) > <7>[ 918.292627] md0_raid1(304): WRITE block 8 on sda1 (2 sectors) > <7>[ 918.292714] md0_raid1(304): WRITE block 8 on sdc1 (2 sectors) > <7>[ 918.308500] md1_raid1(311): WRITE block 8 on sda5 (2 sectors) > <7>[ 918.308588] md1_raid1(311): WRITE block 8 on sdc5 (2 sectors) > <7>[ 923.113309] md0_raid1(304): WRITE block 8 on sda1 (2 sectors) > <7>[ 923.113397] md0_raid1(304): WRITE block 8 on sdc1 (2 sectors) > <7>[ 923.129330] md1_raid1(311): WRITE block 8 on sda5 (2 sectors) > <7>[ 923.129388] md1_raid1(311): WRITE block 8 on sdc5 (2 sectors) > <7>[ 923.332489] md0_raid1(304): WRITE block 8 on sda1 (2 sectors) > <7>[ 923.332545] md0_raid1(304): WRITE block 8 on sdc1 (2 sectors) > <7>[ 923.348507] md1_raid1(311): WRITE block 8 on sda5 (2 sectors) > <7>[ 923.348595] md1_raid1(311): WRITE block 8 on sdc5 (2 sectors) > > Note the 5-seconds pause between each half of this output. > Block 8 seems to be the md superblock (dixit hexdump + description of > md superblock), and "mdadm --examine" shows the "Update time" is being > increased. > Those arrays are in clean state, no synchronisation is happening and > no checking that I know of (I would expect a lot of disk activity). > > Is there any reason why those writes are happening ? > I can imagine a mechanism like filesystem superblock periodic > flushing, but AFAIK it only happens when changes are happening (even > if they are not flushed themselves), and I would expect the same to > happen here. > Is there any knob to control those writes ? > > Regards, 5 seconds suggests a bitmap update. Do you have an internal bitmap? Try to remove it mdadm --grow /dev/md0 --bitmap=none and see if they stop. Then try adding it back with a longer delay mdadm --grow /dev/md0 --bitmap=internal --delay=60 What kernel version are you running? NeilBrown
Attachment:
signature.asc
Description: PGP signature
