Is decreasing the storage size of a DB Instance permitted?
A.
Depends on the RDMS used
B.
Yes
C.
No
Explanation:
“note that you cannot reduce storage size once it has been allocated” Source: http://docs.aws.amazon.com/
AmazonRDS/latest/UserGuideCHAP_Storage.html#CHAP_Storage.FactsAbout
C