High Capacity (HC) Storage Server: The Exadata X9M-2 HC storage server is configured with a combination of hard disks and flash memory, providing a balance of storage capacity and performance.
It includes 12 x 18 TB hard disk drives, which totals 216 TB of raw disk capacity.
For flash storage, it has 4 x 6.4 TB PCIe flash cards totaling 25.6 TB of flash storage. This configuration uses NVMe Flash Accelerator F680 cards optimized for database caching.
The persistent memory in the HC server totals 1.5 TB, enhancing performance for OLTP (Online Transaction Processing) workloads by providing ultra-fast access speeds compared to traditional flash storage.
Extreme Flash (EF) Storage Server: The EF storage server in the Exadata X9M-2 model is an all-flash storage server designed for high IOPS and low latency, making it ideal for performance-intensive workloads.
This configuration contains 8 x 6.4 TB PCIe flash cards, providing a raw capacity of 51.2 TB of high-performance flash storage.
In terms of persistent memory, it includes 756 GB of Intel Optane Persistent Memory. This enhances flash storage performance by offloading data processing directly to persistent memory.
The Exadata X9M-2 storage configurations-both HC and EF-are optimized for different workload requirements. The HC configuration caters to larger datasets needing high storage capacity, while the EF configuration is designed for workloads requiring high throughput and minimal latency.

To drop all celldisks on all the storage servers in an X9M-2 quarter rack, you should use the CELLADMIN account, which has the necessary privileges to perform this task. You can use the CELLCLI command-line interface to drop the celldisks. The best way to do this is by calling CELLCLI on all cells using DCLI (Oracle Database Command Line Interface) which allows you to run commands on multiple servers at once. Alternatively, you can use an administrator-created storage server user with appropriate privileges on celldisk objects by calling CELLCLI on all cells using exadcli. It is not recommended to use the CELLMONITOR account, as it has a more limited set of privileges. It is also important to note that EXACLI is not a valid tool for this task
https://docs.oracle.com/en/engineered-systems/exadata-database-machine/dbmmn/maintaining-exadata-storage-servers.html