When it comes to storing your important data, reliability is key. Hard disk drives (HDDs) are still the most common type of long-term storage for computers, servers and data centers. But not all HDDs are created equal when it comes to durability and avoiding failures. In this comprehensive 5000 word guide, we will explore the key factors that affect HDD failure rates and identify which HDD models and brands tend to be the most reliable for long-term data storage.
What factors affect HDD failure rates?
There are several key architectural, design and usage factors that can impact the annualized failure rate (AFR) for HDDs:
- Drive interface – SAS and FC drives designed for enterprise have lower failure rates than consumer SATA drives.
- Drive capacity – Higher capacity enterprise-class drives tend to be more reliable than lower capacity consumer models.
- Drive rotations per minute (RPM) – 7200 RPM drives have moderately higher failure rates than 10,000 & 15,000 RPM enterprise drives.
- Workload – Drives in heavy workloads and high temperatures are more prone to failure than lightly loaded drives.
- Age – Failure rates steadily increase as drives age, with peak failures typically happening between 3-5 years.
- Manufacturing quality – Failure rates can vary significantly between different drive models, brands and production batches.
Understanding these factors can help predict and compare failure rate profiles for different HDDs.
Failure Rate Metrics
When evaluating and comparing HDD reliability, the most common metric used is annualized failure rate (AFR). AFR represents the percentage of drives that are projected to fail in a given year based on historical failure data.
Bathtub Curve Failure Model
AFR is modeled using the “bathtub curve” reliability engineering model, which visualizes the annual failure rate over the lifetime of a product:
- Early “infant mortality” failures – Manufacturing defects cause high failure rates early in life.
- “Useful life” random failures – Low constant failure rate during most of the functional life.
- Wearout failures – Increasing failures at end of life due to aging and wear.
HDDs typically exhibit this bathtub curve failure distribution, with AFRs lowest during the useful lifespan and higher at the beginning and end of life.
POH – Percentage of HDDs failed
Another reliability metric is the percentage of HDDs failed (POH) within a population. This represents the ratio of actual failed drives versus total drives. A lower POH indicates higher reliability.
MTTF – Mean Time to Failure
MTTF stands for Mean Time to Failure, which is the average time a HDD functions before failure. MTTF is calculated by dividing total accumulated runtime for all drives by total number of failures. A higher MTTF indicates a more reliable drive.
External Factors Affecting HDD Failure Rates
In additional to product design factors, there are several external environmental and usage factors that can influence HDD failure rates:
Temperature and Humidity
Drives exposed to high temperatures or humidity fluctuations have higher failure rates. Enterprise data centers carefully control temperature and humidity to optimize HDD reliability. Consumer PCs and external portable drives are more prone to these environmental risks.
Shock and Vibration
Physical shocks and vibration can damage HDD components leading to premature failures. Enterprise servers and racks use shock mounting techniques to protect drives. Portable external drives are far more susceptible to drops and shock damage.
Power Cycling
Frequent power cycling creates thermal and mechanical stress. Data center drives stay powered on continuously to minimize start/stop cycles. Consumer PCs and external drives go through far more power cycles, which incrementally causes wear.
Duty Cycles
Heavy workloads with sustained read/write activity increases stress and wear on HDD parts. Lightly loaded drives last longer. Enterprise drives rated for heavy 24/7 workloads have lower failure rates when heavily used than consumer drives utilized heavily.
Maintenance and Handling
Rough handling when installing or replacing drives can damage connectors and components leading to premature failure. Enterprise data centers adhere to strict anti-static safety protocols when swapping drives.
HDD Industry Historical Failure Rates
Studying real-world failure data provides insights into overall HDD reliability trends:
Google HDD Study (2007-2013)
A large study of over 100,000 HDDs at Google data centers between 2007-2013 found average annual failure rates (AFR) ranging between 1.7% – 15.4% depending on the drive model. The average AFR across all drives was around 2.5%.
Backblaze HDD Stats (2013-Present)
Backblaze has tracked failure rates for the thousands of HDDs in their storage pods since 2013. Their statistics show steady AFRs between 1.5-2.5% for most models, with some outliers having higher failure rates.
Facebook HDD Study (2010-2015)
Facebook analyzed failure rates for thousands of HDDs used in their data centers between 2010-2015. The median AFR they observed was around 2%, consistent with other studies.
Carnegie Mellon University Study (2002-2015)
A Carnegie Mellon study looking at HDD replacements between 2002-2015 found an average AFR between 2-4% depending on the usage environment and workload. Enterprise drives in servers had lower failure rates than consumer PC hard drives.
AFR Comparisons by Drive Interface
The interface and intended usage category for HDDs has a significant effect on AFR:
Enterprise SAS/FC Hard Drives
SAS and Fibre Channel drives designed for mission critical enterprise environments have the lowest annual failure rates, typically in the 1-2% range. These drives are engineered for high reliability and 24/7 workloads.
Enterprise SATA Hard Drives
Enterprise SATA HDDs are designed for storage servers and data centers. They offer moderately higher reliability than consumer drives with typical AFR of 1.5-3%.
Desktop/Consumer Hard Drives
Standard desktop and consumer HDDs designed for mainstream PCs have slightly higher failure rates in the 3-5% range since they are built for lower workloads and cost targets.
Portable External Hard Drives
2.5″ portable USB hard drives designed for backup and consumer use have the highest failure rates, often over 6% AFR. These drives are susceptible to more shock, vibration and handling damage.
| Drive Type | Typical Annual Failure Rate |
|---|---|
| Enterprise SAS/FC | 1-2% |
| Enterprise SATA | 1.5-3% |
| Desktop/Consumer | 3-5% |
| Portable External | >6% |
Comparing Failure Rates by Manufacturer
Keep in mind that AFRs are averages across entire product lines. Individual models can have higher or lower failure rates. Overall HDD reliability tends to be fairly comparable between the major enterprise manufacturers:
Hitachi/HGST Hard Drives
Hitachi drives historically have had slightly lower than average failure rates, especially their enterprise models. Their consumer models have AFR comparable to competitors. HGST drives maintain this legacy of high reliability.
Western Digital Hard Drives
Western Digital has a broad range of enterprise, server and consumer hard drives. Their Deskstar and RE server series drives offer solid reliability while consumer models have moderately higher failure rates.
Seagate Hard Drives
Seagate is on par with other major manufacturers for enterprise drive reliability. Some Backblaze reports have shown elevated failure rates for certain desktop Seagate models compared to competitors.
Toshiba Hard Drives
Toshiba designs reliable enterprise and data center hard drives. Some of their consumer notebook and desktop models have demonstrated higher than average failure rates in a few studies.
In summary, all the major manufacturers produce drives with similar AFRs on average, but specific models can show better or worse reliability.
Ideal HDD Models for Low Failure Rates
Based on all the data and comparisons, these drive models consistently demonstrate the lowest annual failure rates ideal for critical storage:
Hitachi Ultrastar Series
The Hitachi Ultrastar series are top-tier enterprise HDDs designed for the highest reliability with low 1-2% AFR. For example, the Ultrastar DC HC620 has a stellar 0.35% AFR.
Western Digital RE Series
WD’s RE line are enterprise SATA drives built for 24/7 operation and have consistently low 1-3% AFR even under heavy workloads. The WD RE 4TB model has one of the lowest failure rates around 1.2%.
Seagate Exos X Series
The Seagate Exos X is their flagship enterprise drive engineered for maximum reliability with low 1.6% AFR and a 2.5M hour MTBF. It maintains excellent reliability under heavy workloads.
HGST Ultrastar He Series (Helium)
HGST’s helium-filled Ultrastar HeSeries delivers exceptional density with high reliability and just 1-2% AFR. It provides low failure rates even at massive 10TB+ capacities.
Conclusion
To achieve optimal HDD reliability with failure rates under 2% AFR, enterprise class SAS, FC or SATA drives designed for 24/7 operation are recommended. Top choices include Hitachi Ultrastar, WD RE, Seagate Exos X and HGST Helium drives. For less critical storage, recent model desktop/consumer drives from the major manufacturers offer reasonably low failure rates around 3-4% AFR. With their higher susceptibility to environmental factors, portable external HDDs have significantly higher annual failure rates typically over 6% AFR. Carefully selecting enterprise-class HDD models engineered for high reliability is key to minimizing failures and data loss.