In this example, 5 is the repetition factor and (2 3 4) is the list of initial values for the array elements. If the list consists of only a single item, then you can omit the parentheses. For example ...

I have this card and according to the readme's (don't remember which one) this is normal after expanding the array in RAID5. It is actually initializing the redundancy data, not the complete array ...