Raspberry Pi = Plex + NAS server
update: So far the Raspberry Pi 3 is not powerful enough for me. It takes several minutes for a movie to start streaming a mp4 file to ATV in the same LAN. It just not good enough, yet.
My mac is getting old, can't work on it as CPU go up to 100% while family is watching.
The plan is to move the Plex server to Raspberry Pi. It should be a economical replacement for the media function.
The solution seems mature, references can be found easily. I ordered the new board, prepare the SD card, and format my 4TB external USB drive to ext4 format. As the board arrives, I will get my hand dirty and note the process here.