Once you have decided on the total amount of disk space to use for each cluster, you must break that total disk space for each cluster down into disk space that is used for the three disk groups within each cluster:
DATA
RECO
DBFS
The DBFS disk group is normally assigned a substantially smaller amount of total disk space than the other two disk groups. You can also designate the DBFS disk group as UNUSED, if necessary.
For example, if 12 TB of space is available for each cluster, you must carve that 12 TB of space up so that the combined disk space used by all three disk groups is 12 TB or less.