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, -- Vincent Pelletier -- 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
