What is the smallest unit of data that Isilon OneFS will write to disk?

What is the smallest unit of data that Isilon OneFS will write to disk?

A.
4 KB

B.
8 KB

C.
16 KB

D.
128 KB

Explanation:
http://www.scribd.com/doc/150129112/Isislon-Course-Student-Guidev (page 52)