About RAID Calculator
What This Calculator Does
Our RAID calculator is a professional-grade tool designed for storage administrators, NAS users, and IT professionals who need accurate calculations for RAID array configurations. Unlike simple calculators that only show usable capacity, we provide comprehensive analysis including rebuild times, URE (Unrecoverable Read Error) risk, failure tolerance, cost analysis, and power consumption.
We support all major RAID levels: 0, 1, 1E, 10, 5, 50, 5E, 5EE, 6, and 60 - with accurate formulas validated against industry standards and vendor documentation.
Why Accurate RAID Calculations Matter
Choosing the wrong RAID level or miscalculating capacity can lead to data loss, wasted storage budget, or inadequate performance.
Storage planning requires understanding trade-offs between:
- Capacity efficiency - How much usable space you get from raw drives
- Redundancy - How many drives can fail without data loss
- Performance - Read/write speeds and I/O patterns
- Rebuild risk - Probability of data loss during array rebuild
- Cost per TB - Total investment vs usable storage
Formulas & Methodology
All calculations are based on industry-standard formulas. For transparency, here's how we calculate key metrics:
Usable Capacity Formulas
Usable = Σ(drive sizes) All capacity is usable, no redundancy
Usable = (N / 2) × min_drive_size 50% capacity for complete mirroring
Usable = (N - overhead) × min_drive_size N-1 for RAID 5, N-2 for 5E/5EE (integrated spare)
Usable = (N - 2) × min_drive_size Two drives worth of capacity for dual parity
Usable = (N / G) × (G - parity) × min_drive_size G = group size, parity = 1 for RAID 50, 2 for RAID 60
Rebuild Time Calculation
Rebuild Hours = (Drive Size TB × 1,024² MB) / (Rebuild Speed MB/s × 3,600)
Based on effective throughput after RAID overhead. Default 100 MB/s represents typical sustained rebuild speed for consumer NAS.
URE (Unrecoverable Read Error) Risk
P(URE) = 1 - (1 - URE_rate)^bits_to_read
Where bits_to_read ≈ Drive_Size_TB × 8 × 2⁴⁰
Standard consumer HDD URE rate: 10⁻¹⁴ (1 bit error per 12.5 TB read). Enterprise drives: 10⁻¹⁵ or better.
Annual Data Loss Probability (Simplified)
P(ADL) ≈ AFR% × (Active_Drives - Failure_Tolerance) × (Rebuild_Hours / 8,760)
Simplified heuristic for UI purposes. Actual MTTDL calculations are more complex and require detailed workload analysis.
Assumptions & Limitations
Important: This calculator provides estimates, not guarantees
Real-world results vary based on hardware, firmware, workload patterns, and environmental factors. Always validate with your specific hardware vendor.
- Mixed drive sizes: Calculations use minimum drive size across the array (standard RAID behavior)
- Overhead: Filesystem overhead (5-10%) not included - calculations show raw RAID capacity
- Rebuild speed: Actual speeds vary by hardware, load, and RAID controller capabilities
- URE rates: Based on manufacturer specs; real-world rates may differ
- Nested RAID: RAID 50/60 assume equal group sizes and standard configurations
- Performance: Read/write speed depends on controller, cache, workload - not calculated here
Data Sources & References
Our formulas and assumptions are based on:
- SNIA (Storage Networking Industry Association) standards
- Vendor documentation from Synology, QNAP, Dell, HPE
- IEEE and USENIX storage research papers
- HDD/SSD manufacturer datasheets (Seagate, WD, Toshiba, Samsung)
- Industry best practices from storage administrators
Who Built This
This calculator was built to provide the storage community with a free, accurate, and comprehensive RAID planning tool. Unlike basic calculators that only show capacity, we wanted to help users understand the full picture: risks, costs, and trade-offs.
The tool is open-source, continuously improved based on user feedback, and designed to support both home NAS users and enterprise storage administrators.
Feedback & Contributions
Found an issue? Have a suggestion? We welcome feedback to make this tool better.