How to to direct files to different discs?

[Tricky]

In the brief time i was able to do some configuration of my F5-221 NAS (faulty sent back for replacement) i had added three HDDs and configured two to RAID1 and one as a single disc and would have been adding two more as single discs later and in the process i couldn't find a way to direct where a file i wanted to save was to reside IE the RAID1 or the single disc so the question is how do i do this in future when i have one RAID1 and three single discs?

[TMSupport]

The files stored in TNAS are kept in different folders, and created shared folders could be assigned to different volumes. And volumes are created on different Storage pools.
As for your existing HDDs, the two HDDs created as RAID1 would be a storage pool; and so is the single disk.
So you have two storage pools now, you can create a volume (or volumes) on each storage pool. Then create shared folders on each volume so that you can know which files are kept on which disk.