I've got a raid 5 array in my home server with 5.4 tb of effective usable space. I wanted a backup solution that could mirror that data to a NAS also running raid 5.

The array in the server is just a file storage array, the OS is running of a SSD so abrely any files in use.

I tried 7 utilities including FreeFileSync and Synctoy.
Both did there job. FreeFileSync was just a lot better and faster at it. Synctoy would take a very long time to scan for changes and would create "tasks" on a per file basis to copy them to the NAS. FreeFileSync did the same task in barely a minute which a more or less 10 times faster compared to synctoy. Actual transfer speed were more or less the same though