Can anyone please advice me on how to implement a FIFO functionality on a RAID 0 HDD. I want the old files to be over written after the space of the HDD is zero, so that the RAID acts like an infinite loop. Any ideas on how this is accomplished?
You can't do that on RAID level.
Nor can you do it on the file system level as I am not aware of any file system that supports this.
You need to have a piece of software do that for you - sit there, monitor the disk usage, keep an index of all files by age and then remove by age when the disk space is exhausted.