I had a RAID5 array consisting of 3x5TB disks assembled using
mdadm. On top of that, I created a
LUKS/dmcrypt encryption layer and formatted the encrypted device with
ext4. I want the disks to spin down in case of inactivity.
Everything worked fine for several months, the disks were spinning down after a minute of inactivity. Now, I added a fourth 5TB disk of the same kind to the array by
sudo mdadm --add /dev/md0 /dev/sdb1, then I grew the array onto that disk (
mdadm --grow /dev/md0 --raid-devices=4), and finally grew the filesystem with
sudo fsck -f /dev/mapper/raid5 and
sudo resize2fs /dev/mapper/raid5.
No errors occured, and the array is now 5TB larger. But the disks are not spinning down anymore. The machine runs 24/7, is not using the disks, but despite waiting a couple of days, the disks are still running all the time.
iotop shows frequent occurences of
ext4lazyinit, which pops up for less then a second every few seconds. I didn't notice that before growing the filesystem. So probably it's that tasks keeping the disks awake? But how can I force
ext4lazyinit to complete it's task?