NetApp
Cluster : Storage > Disks : Understanding disks : Available disk capacity by disk size

Available disk capacity by disk size
To maintain compatibility across different brands of disks, Data ONTAP rounds down ("right-sizes") the amount of space available for user data.
Because of right-sizing, informational commands such as sysconfig show a lower number for available space than the disk's rated capacity (you use rated capacity if you specify disk size when creating an aggregate). The available disk space is rounded down as shown in the following table.
Note: For this table, GB = 1,000 MB.
The capacity numbers in this table do not take into account the 10 percent of disk space that Data ONTAP reserves for its own use.