How does SAP HANA ASYNC replication behave, and what is its main trade-off?

In SAP HANA active/active read-enabled, how is read-access memory capped, and what is the default?

What constraint does the active/active read-enabled option place on SAP HANA version upgrades?

In SAP HANA system replication, what mode does the secondary run in, and what does each secondary service do?

What is storage replication in the SAP HANA context, and why is the secondary HANA instance inactive during it?

In SAP HANA system replication, when does the secondary need to re-register after the primary is recovered?

Which SAP HANA script gives a takeover recommendation, and what three results can it return?