How does SoftRAID use SMART to predict disk failure?

SoftRAID continuously monitors your disks using SMART (Self-Monitoring, Analysis, and Reporting Technology), a built-in monitoring system in modern hard drives and SSDs that tracks drive health and reliability indicators.

When SMART monitoring occurs

• On startup: Every time you launch the SoftRAID application
• On Mac restart: SoftRAID Monitor checks SMART status automatically
• Every 24 hours: Continuous monitoring while your Mac is running

How SMART predictions work

Each time SoftRAID checks SMART status, it looks for two types of indicators:

• 1. SMART test failures: Drives that have already failed the SMART self-test and need immediate replacement
• 2. Predictive indicators: Specific SMART parameters that research has shown strongly correlate with imminent drive failure

The science behind SMART predictions

SoftRAID’s failure prediction is based on extensive research from multiple large-scale drive reliability studies:

Google’s landmark study (2007): Analysis of over 100,000 drives identified key SMART parameters that correlate with drive failure. For example, after the first scan error, drives were found to be 39 times more likely to fail within 60 days than normal drives.

Key finding from Google: 36% of failed drives showed no SMART warnings before failure, meaning SMART is valuable but not perfect—it can warn you about many problems but will miss others.

Backblaze ongoing data (2013-present): Continuous monitoring of 300,000+ drives in production data centers provides real-world reliability data. Recent 2024 data shows an overall annual failure rate of 1.57%, with specific drive models and ages showing varying failure patterns.

Most critical SMART parameters for failure prediction:

• Reallocated sectors: A disk with even a single reallocated sector is 20-60 times more likely to fail within 60 days than a normal drive
• Uncorrectable sectors: Indicates the drive cannot reliably read data
• Pending reallocations: Sectors waiting to be reallocated
• Failed reallocations: The drive attempted to reallocate sectors but failed

Beyond SMART monitoring

SoftRAID also tracks I/O errors (disk read/write failures) which aren’t part of SMART but can indicate hardware issues with the drive, enclosure, or communication problems.

What you should know

SMART is highly valuable but not perfect: When SMART identifies a problem, it’s a strong indicator of impending failure. However, some drives will fail without any SMART warnings, which is why regular backups remain essential regardless of SMART status.

Act on SMART warnings immediately: If SoftRAID reports a SMART predicted failure or failed SMART test, plan to replace that drive as soon as possible. The research shows these warnings are strongly correlated with drive failure within weeks or months.