How do you manage old files on a CCTV system?

I have a few cameras that send video recordings and images via Unraid's FTP server to a UD disk. Eventually that disk will fill up and I manually go in to delete the oldest files which is cumbersome. I know pretty much all NVR systems have a function to delete the oldest files as storage space is used up but how are people using systems like Blue Iris / dockers (Shinobi/Zoneminder) / or even just a spare disk like me, manage their storage space? 

I've never used Blue Iris so I'm not sure if that offers a similar feature of removing the oldest files automatically.