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Chapter 4: Endurance & Reliability
Reliability is about expected lifespan, not just warranty length. This chapter explains TBW, DWPD, MTBF, and how to interpret real-world failure data.
TL;DR
Consumer SSDs often quote 300–600 TBW per 1TB, while HDD reliability varies by model and workload. For critical data, prioritize backups over a single drive’s MTBF.
Key Takeaways
- TBW and DWPD indicate write endurance; higher values matter for heavy workloads.
- MTBF is statistical, not a promise for individual drives.
- Backups reduce risk more than choosing one “best” drive.
What do TBW and DWPD mean?
| Metric | Meaning | Example |
|---|---|---|
| TBW | Total writes over warranty | 600 TBW for a 1TB SSD |
| DWPD | Drive writes per day | 1 DWPD = 1TB/day for 1TB drive |
Rule of thumb: TBW = Capacity × DWPD × 365 × Warranty Years.
How to interpret MTBF and AFR
- MTBF (Mean Time Between Failures) is a statistical average across large populations.
- AFR (Annualized Failure Rate) is easier to compare for real-world models.
Backblaze reports real-world AFRs across hundreds of thousands of drives, which is useful for fleet-level comparisons.
Decision Framework
- Write-heavy workloads (video, databases)? Choose higher TBW/DWPD SSDs.
- Archive or backup? HDDs are fine but rely on redundancy.
- Mission-critical data? Use RAID + offsite backups regardless of drive type.
Data Appendix
| Data point | Source | Date | Confidence |
|---|---|---|---|
| TBW/DWPD guidelines | Storage Disk Prices | 2026-01 | B |
| Real-world failure rates | Backblaze | 2025-11 | B |
References
This article was researched with AI assistance and human-edited for accuracy. We have not independently tested the products mentioned unless explicitly stated. Last updated: 2026-02-11.