On the latest release of truenas scale, there is read activity on HDD that is not the boot drive, does not have the system dataset or the application dataset every 5 minutes. There is currently no other data on the HDD with the read activity, it was only added to the pool. Turning off S.M.A.R.T on the drive stops the every 5 minute read activity. It then triggers a read activity with a warning about S.M.A.R.T not functioning or being disabled every 30 minutes.
Forum Thread with another user running into a similar situation. Other user found that the same activity doesn't occur with truenas core.
There's another forum thread with a user with a similar issue here: Forum Thread