In the meantime, I created a new server set up. Although it is not as energy efficient as the previous one, but 18 watts are acceptable for a 24/7 runtime.
It is running with a Quad Core Celeron J4205 with 2.6GHz and 16GB DDR3-1833. As a harddrive there are one 64GB SSD and one 3TB raid 1. The server case itself features 4 HotPlug slots for easy changing harddisks. This setup will give me some flexibility for the future :-)
I use openSUSE as my operating system. The reason is my personal preference and habit. I use SuSE since version 4.3. I changed almost directly from my formerly used Amiga OS. :-)
The hardware cost about 570 € and the parts list is as follows.
Who does not need Raid 1 can fall back on my previous configuration.
It is a completely fanless system (18cm x 3,6cm x 18cm) which is running on a Intel Atom N2800 and it consumes 10 watt. Additionally it has one 64GB SSD. The performance is more than sufficient. The waste heat is small enough to put it in a closed cabinet. Without a fan and together with the SSD there are no moving parts to wear out.
The parts list is as follows.
The following services are provided on the server: