I turned off the “Put hard disks to sleep when possible” option. That solved the problem of array disk spin down. Turning off “Put hard disks to sleep when possible” also have solved the issue of the RAID volume not responding. Maybe MacOS does something wrong when it tells hard disks to go to sleep. Now I am able to intensively process small amounts of video without any issues with the Areca RAID volume.
Tags: ARC-8050U3-6, macOS