How much usable RAID storage will these drives provide?
For standard RAID, start with the active drive count and the smallest active drive, subtract mirror or parity capacity, then show hot spare, reserve and decimal-TB to binary-TiB effects separately.
Method
The planner uses transparent standard RAID formulas and caps every active drive at the smallest active size. Reserve is editable and TB-to-TiB conversion is shown, not hidden.
Important limitation
It does not model SHR, RAIDZ, Unraid, controller metadata, rebuild time, performance or failure probability. RAID is not a backup.