Consider the following example scenario:
Oracle SuperCluster M7, with three X6-2L Exadata Storage Servers
12 high-capacity (8 TB) disk drives in each Exadata Storage Server
Each Exadata Storage Server set at normal (double-mirrored) redundancy
Using the information from the section Determine the Available Existing Storage Capacity, you have 120 TB of usable storage capacity available for the Exadata Storage Servers in your Oracle SuperCluster M7.