According to the Oracle Exadata Database Machine X9M Implementation Essentials Official Text Book, the maximum DRAM capacity you can expand an X9M-2 DB Server is 1024GB. This is the maximum amount of DRAM that can be installed in the server. The specific steps for adding DRAM are outlined in the book and can be referenced here: https://docs.oracle.com/cd/E80920_01/E80920/html/x9m_hardware_memory.html.

1. ZFS Storage Appliance (ZFSSA) can't connect directly to the Exadata 100Gb RoCE network switches. ZFSSA uses Fibre Channel protocol to connect to the Exadata storage cells. C. When backing up multi-rack systems, sharing Exadata X9M switches is not recommended. Each rack should have its own switches to minimize the risk of data loss due to switch failure.
Review the safety guidelines.
Unpack Oracle Exadata Rack.
Let the Exadata acclimatize for 24 hours.
Place Exadata in its allocated space.
Stabilize the Exadata Rack.
Power on Exadata PDU A.
Power on Exadata PDU B.
This order ensures that the necessary safety precautions are taken before installing the Exadata Database Machine, and that the machine is allowed to acclimate to its new environment before being powered on.

[1] Oracle Exadata Database Machine X9M Implementation Essentials Official Text Book [1][2], Chapter 4: Oracle Clusterware [2] Oracle Exadata Database Machine X9M Implementation Essentials Official Text Book [1][2], Chapter 8: Oracle Exadata Storage Server Software [3] Oracle Exadata Database Machine X9M Implementation Essentials Official Text Book [1][2], Chapter 9: Oracle Exadata Storage Server Infrastructure
https://www.oracle.com/technetwork/database/availability/exadata-backup-recovery-bp-3633870.pdf

The two statements that are true about enabling write-back flash cache are:
When enabling write-back flash cache in a rolling manner, DBCLI should be used to inactivate the grid disks on all cells first.
Before write-back flash cache is enabled, you need to drop the Flash Cache first.
The Oracle Exadata Database Machine X9M Implementation Essentials Official Text Book states that "when enabling write-back flash cache in a rolling manner [1], grid disks need to be inactivated on all cells before enabling write-back flash cache". It also states that "before write-back flash cache can be enabled, the existing flash cache must be dropped".