Reading a target-capacity result
Required drives is the minimum count that satisfies the selected RAID rules and allowance. Total raw capacity is drive count × capacity per drive before parity or mirroring.
Options when bays are insufficient
If the selected RAID exceeds the NAS bay limit, the result shows the missing bays and the minimum per-drive capacity needed in the available bays. It also compares other RAID levels that fit with the same drives, but do not reduce fault tolerance based on capacity alone.
What the calculator assumes
Every drive has the same capacity. RAID 5 spends one drive-equivalent on parity, RAID 6 spends two, and RAID 10 mirrors half of the drives. Adding RAID 1 mirrors does not increase usable capacity.
Mixed drives and vendor-specific RAID
Layouts such as SHR depend on drive sizes and implementation details. Recheck them with a vendor tool such as the official Synology RAID Calculator.