Hello, Norro21. You are correct. Without proper ventilation, overheating is guaranteed. This is to ensure the proper airflow in the array. Here's a quick 4 minute video on exactly that: www.youtube.com/watch You are welcome to "fill them with any old spare drive temporarily", but there's no way we could guarantee the response from the array or the alerts in the GUI. (chances are great that it would be just fine) Have a great rest of the day!
There is a warning on the 3060e to make sure that the front row of each tray is filled with blanks or drives.  The manual simply says that the minimum number of drives is 20.The unit will ultimately be deployed with more but I need to test a unit with the drives I have at hand (less than 20).Is this requirement just for airflow?  In which case I can fill them with any old spare drive temporarily.
Less than 20 drives in a 3060e storage enclosure