Why does SAP HANA have a persistence storage layer that is disk-based? There are 2 correct answers to this question.

Why does SAP HANA have a persistence storage layer that is disk-based? There are 2 correct answers to this question.
A . To generate indexes for the column store
B . To persist in-memory data
C . To enable data recovery if the power fails
D . To allow row store operations

Answer: B,C