I have the 4TB NAS - do need to leave some space as overhead so the NAS can do disk clean up? If so, how much is recommended - 25%? Or can the full usable space be utilized, which is ~ 3.8 TB effective.
Hello and welcome to the WD Community.
When you say a clean up, are you referring to a reset or factory restore?
He probably means defragment.
In which case, look up ‘ext4 defragmentation’.