I currently have a dedicated BI Machine as follows:
Dell Optiplex 9020
i7-4790
8GB RAM
250GB SSD
4TB WD Purple
4TB WD Blue
5 cameras of various specs
Currently recording at approx 2040 kB/s and 170 MP/s, CPU is at 13%.
I run everything thing at moderate FPS (8-13 FPS) to get more historical...