About this tool

ZerkDrive — RAID Capacity Calculator helps you quickly estimate usable capacity, redundancy and overhead for common RAID levels. It assumes identical drive sizes within an array and focuses on simple sizing rather than vendor-specific features.

Formulas

• RAID 0: usable = N × size, min disks: 1, fault tolerance: 0
• RAID 1: usable = 1 × size (mirrors), min disks: 2, fault tolerance: N − 1
• RAID 5: usable = (N − 1) × size, min disks: 3, fault tolerance: 1
• RAID 6: usable = (N − 2) × size, min disks: 4, fault tolerance: 2
• RAID 10: usable = ⌊N / 2⌋ × size (N must be even, min 4), fault tolerance: one drive per mirrored pair

Unit conversions

Vendors advertise in TB (10¹² bytes), while operating systems often show TiB (2⁴⁰ bytes). The calculator reports both. Actual filesystem capacity can be slightly lower due to metadata and reserved blocks.

Tips

• Plan for rebuild windows: larger drives mean longer rebuilds, so consider RAID 6 or hot spares.
• Mixing drive sizes reduces effective capacity to the smallest drive; avoid heterogeneous sets.
• Backups are still required; RAID is not a backup.

Last updated: 2025-09-13

Contact: hello@zerkdrive.digital