RAID Recovery Feasibility Calculator
Estimate the probability of successful RAID data recovery based on your array configuration, number of failed drives, and individual drive health scores.
Formulas Used
1. Structural Feasibility:
Feasible if failed_drives ≤ fault_tolerance
RAID 0: 0 | RAID 1: N−1 | RAID 5: 1 | RAID 6: 2 | RAID 10: ⌊N/2⌋
2. URE Probability during Rebuild:
P(URE) = 1 − (1 − URE_rate)bits_to_read
where bits_to_read = surviving_drives × drive_size_TB × 1012 × 8
3. Drive Health Factor:
H = exp( (1/n) × Σ ln(health_i / 100) ) — geometric mean of health scores
4. Rebuild Survival Probability:
P(survive) = (1 − AFR/8760)rebuild_hours × surviving_drives
Assumes 4% annualised failure rate (AFR) for drives under rebuild stress.
5. Overall Recovery Probability:
P(success) = (1 − P_URE) × H × P(survive) [0 if structurally infeasible]
6. Recoverable Data:
Recoverable_TB = Array_Capacity_TB × P(success)
Assumptions & References
- URE (Unrecoverable Read Error) rates sourced from manufacturer specifications: consumer HDDs ~10−14, enterprise HDDs ~10−15, SSDs ~10−16–10−17.
- A 4% annualised failure rate (AFR) is used as a baseline for rebuild-period drive stress, consistent with Backblaze HDD reliability reports (2023).
- Drive health score is a user-supplied estimate (e.g., from SMART data, sector error counts, or physical assessment).
- RAID 10 fault tolerance assumes worst-case: one failure per mirrored pair is tolerable; two failures in the same pair are not.
- Array capacity formulas follow standard RAID definitions (no RAID controller overhead).
- This calculator does not account for filesystem corruption, controller failure, or partial stripe writes (RAID 5 write hole).
- References: Patterson, Gibson & Katz (1988) "A Case for Redundant Arrays of Inexpensive Disks (RAID)"; Elerath & Pecht (2007) "Enhanced Reliability Modeling of RAID Storage Systems".