If the amount of data you need protected is small, you will be much better off with a scheduled 1:1 backup using programs like SyncToy.
RAID with parity only makes sense on a larger scale.
Now, FlexRAID can very effectively act as a 1:1 backup program through a Snapshot RAID configuration which has only a single DRU composed of the folders you want to duplicated and a PPU space large enough for the data replication.
So, if you have more than one drive, put the data to be duplicated on one drive and RAID it again some free space in one of the other drives.
The space used for parity on the target drive will only be as large as the data size being mirrored.
The value in this approach would be if you wanted the integration plus FlexRAID’s powerful scheduling engine. I have actually had better luck doing 1:1 backup using FlexRAID than SyncToy (as far as behavior reliability), but programs like SyncToy let you recover in a much simple fashion.
Note that using FlexRAID’s expression language, one can leverage its scheduler to call onto an external program (like SyncToy) to do the mirroring. However, this is an advanced topic reserved for power users.