C: The decompression process typically takes place on the Oracle Exadata Storage Server in order to maximize performance and offload processing from the database server.
E: A logical construct called the compression unit is used to store a set of hybrid columnar compressed rows. When data is loaded, column values for a set of rows are grouped together and compressed. After the column data for a set of rows has been compressed, it is stored in a compression unit.
F: What happens when I update a row on compressed tables? What about locks?
Note: Oracle's Hybrid Columnar Compression technology is a new method for organizing data within a database block. As the name implies, this technology utilizes a combination of both row and columnar methods for storing data. This hybrid approach achieves the compression benefits of columnar storage, while avoiding the performance shortfalls of a pure columnar format.

CD: That data remains compressed not only on disk, but also remains compressed in the Exadata Smart Flash Cache, on Infiniband, in the database server buffer cache, as well as when doing back-ups or log shipping to Data Guard.
E (not B): Use the Write-Back Flash Cache feature to leverage the Exadata Flash hardware and make Exadata Database Machine a faster system for Oracle Database Deployments. Write-through cache mode is slower than write-back cache mode. However, write-back cache mode has a risk of data loss if the Exadata Storage Server loses power or fails.
F: Storage indexes are not stored on disk; they are resident in the memory of the storage cell servers.

C: Step 1:
Run the following command to check if there are other offline disks
CellCLI> LIST GRIDDISK ATTRIBUTES name WHERE asmdeactivationoutcome != 'Yes' If any grid disks are returned, then it is not safe to take the storage server offline because proper Oracle ASM disk group redundancy will not be intact.
E: Step 2:
Inactivate all the grid disks when Oracle Exadata Storage Server is safe to take offline using the following command:
CellCLI> ALTER GRIDDISK ALL INACTIVE
Taking the storage server offline when one or more grid disks are in this state will cause Oracle ASM to dismount the affected disk group, causing the databases to shut down abruptly.

Intelligent Data Placement enables you to specify disk regions on Oracle ASM disks for best performance.
Using the disk region settings, you can ensure that frequently accessed data is placed on the outermost (hot) tracks which have greater speed and higher bandwidth. In addition, files withsimilar access patterns are located physically close, reducing latency. Intelligent Data Placement also enables the placement of primary and mirror extents into different hot or cold regions.
References: https://docs.oracle.com/cd/E11882_01/server.112/e18951/asmdiskgrps.htm#OSTMG10072