Each Exadata X6 storage cell comes with 12 x 8TB SAS 7200 RPM disks with a total Raw capacity of 96TB for each cell. Now if you want to see how to calculate the Normal or High redundancy for example of a Quarter Rack it is not simply taking the raw storage amount divided by 2 for Normal redundancy and 3 for High redundancy. The formula is below and I confirmed this with Oracle Support as well.
Please note: The amount of storage that needs to be reserved to recover from the failure of a disk is 15% of the cell disk capacity.
# cellcli -e list celldisk attributes name,size
CD_00_internal 7.1192474365234375T
...
The calculation is as follows -
Size of one disk : 7.1192474365234375TB
Disks per cell node : 12
No of cell nodes : 3
Total size of Disk : 7.119TB * 12 * 3 = 256.284TB
Normal Redundancy = [ Total size of Disk / 2 ] * .85
= [ 256.284TB / 2 ] * .85
= 128.142TB * .85
=> 108.9207TB or 109TB [ The value in the Exadata X6 data sheet ]
High Redundancy = [ Total size of Disk / 3 ] * .85
= [ 256.284TB / 3 ] * .85
= 85.428TB * .85
=> 72.6138TB
A table below also shows this information to easily see the values on the different size configurations.
