I have just put together a TrueNas scale box. Storage config: 2x Toshiba N300 16TB NAS drives in a zfs mirror array.
I have moved the system data to my boot SSDs, don’t have any apps installed and don’t have any pool set for apps.
I noticed that even when doing nothing, I hear the sound of drives working every few seconds. What is it actually doing? Is this normal behavior? How do I stop this as it can be annoying
It may be what you want is to enable HDD standby, which will “spin down” the drives when not in use
Storage → Disks → Select your disk → HDD Standby
That being said, depending on your use case, there may be very little standby time. And it has performance implications: slow reads/writes due to the corresponding “spin up” time, but also can reduce power usage for long idles.
Those are probably the system logs being flushed to disk every few seconds. Look into General → System Dataset. Enable the checkmark for the Syslog and choose a pool that is not based on hard drives. Usually when you have installed Truenas to an SSD, this SSD is its own pool and you can select it in this submenu. After you apply these settings the logs will be written to your SSD instead of being flushed to the disc array.
The settings you mentioned are already set this way.
It is already enabled
Sounds like the drives being woken for the ZIL to flush writes to the ZFS pool and then going back to idle/sleep every 5 seconds. Which would be normal behavior.
Your pool gets writes from somewhere and ZFS is writing those to disk every 5 seconds.
Simply installing the apps and choosing a pool for k3s and docker creates a dataset and logs.