You must drop all celldisks on all the storage servers in an X9M-2 quarter rack...

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