What is the recommended reserve LUN size?

A colleague plans to use VNX Snapview Snapshots to make local copies of four data
warehouse LUNs. The LUNs to be snapped are:
10 GB
20 GB
30 GB

100 GB
What is the recommended reserve LUN size?

A.
4 GB

B.
8 GB

C.
2 GB

D.
16 GB