SMART drive monitoring
Also known as: S.M.A.R.T., SMART data, Self-Monitoring Analysis and Reporting Technology, drive health monitoring
SMART (Self-Monitoring, Analysis and Reporting Technology) is a feature built into hard drives and SSDs that tracks indicators of drive health, such as reallocated sectors, read errors, temperature, power-on hours, and, for SSDs, remaining wear.
Software can read SMART data and warn when a drive shows signs of failing. While SMART warnings are valuable and should be taken seriously, many drives fail without any warning, so monitoring is no replacement for backups.
SMART drive monitoring, explained at three levels
At home
SMART is like a car's dashboard warning lights for your drive. The car constantly measures things like oil pressure and engine temperature, and lights up a warning when something crosses a limit. A drive does the same, counting bad spots, read errors, temperature and wear, and flagging trouble when a count gets too high. Like a car, though, some failures happen with no warning light.
At work
SMART is a self-monitoring feature built into hard drives and SSDs that records health indicators such as bad sectors, read errors, temperature and, for SSDs, remaining wear. Monitoring tools read these figures and alert IT when they start getting worse. Businesses care because it turns some sudden drive failures into planned replacements, although many drives still fail without warning, so backups remain essential.
At home
Drives keep a running health log about themselves. SMART tracks counters such as how many sectors have gone bad and been swapped for spares, how many reads needed retries, the temperature, power-on hours and, for SSDs, how much of their write endurance has been used. Tools read those counters and compare them with thresholds the manufacturer set. When a key counter crosses its limit, the tool warns you that the drive may be failing.
At work
Important hard drive attributes include reallocated sector count, current pending sectors, offline uncorrectable sectors and UDMA CRC errors, which usually point to cables. For SSDs, watch percentage used or wear levelling count, available spare and media errors, reported through the NVMe health log. Each manufacturer interprets attributes differently. RMM tools, NAS devices and monitoring agents can alert when values change, which is more useful than waiting for an overall pass or fail.
At home
SMART cannot predict every failure. Large studies of data centre drives, such as Backblaze's, found many failed drives showed no SMART warnings beforehand, while some drives with warnings kept running for years. Sudden failures, such as electronics dying, give no notice at all. Clicking sounds or sudden slowness can signal trouble even when SMART looks fine. In my view, trust the symptoms and back up right away, rather than waiting for a red warning.
At work
Collect SMART data across the fleet and alert on changes in key attributes, not only threshold failures, since rising reallocated or pending sector counts predict failure better than the overall status. Track SSD wear on heavily written systems such as databases and logging servers, and replace drives proactively in arrays when attributes trend badly. Treat SMART as one signal alongside redundancy and backups, since it misses many failures entirely.
Real-world examples
At home
Aisha's laptop felt slow, so she checked its SMART status. It showed a growing number of bad sectors, so she backed up and replaced the drive that weekend.
At work
Marcus's Winnipeg MSP set its RMM tool to alert on SMART warnings. It flagged a failing drive in a client's server days before it died.
Common confusions
- If SMART says a drive is healthy, it won't fail. — Many drives fail without warning. SMART catches some problems, not all.
- SMART only matters for old hard drives. — SSDs report SMART data too, including how much of their write lifespan remains.
For analysts
I'd include drive health monitoring in managed service agreements. It's low cost and turns some emergencies into planned replacements.
History & origin
In the early 1990s, IBM and Compaq developed drive failure prediction features, and the industry combined these efforts into SMART around 1995, later included in ATA storage standards. Operating systems and utilities gradually added SMART monitoring. A large 2007 study by Google engineers of over 100,000 drives found some SMART errors strongly predicted failure, but many failed drives showed no SMART warnings at all. Cloud backup company Backblaze began publishing drive failure statistics in 2014, using SMART data, offering the public rare insight into real-world reliability. In my view, SMART is a smoke detector: helpful, but you still need fire insurance.