How Does Isilon SnapshotIQ Use Storage for Snapshots

How does Isilon SnapshotIQ use storage for snapshots?

A) Through Changed Block Tracking and only changed data blocks are saved
B) Works on the file level and saves the entire file no matter what has changed
C) Works with 4 KiB blocks and will always use that amount of storage, no matter what has changed
D) Through Changed Block Tracking and always uses a 4 KiB block, even if the data changed is less than that amount