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What is SMART (how a drive checks its own health)?

In one sentence: The health logbook a hard drive or SSD keeps about itself, counting worn-out spots, read retries, temperature and wear, so tools can warn you before it fails.

A little more

SMART (Self-Monitoring, Analysis and Reporting Technology) is a little logbook that hard drives and SSDs keep about their own health. The drive counts things like how many hours it has been switched on, how often it had to retry a read, how many worn-out spots it has swapped for spare ones (reallocated sectors), how hot it runs and, on an SSD, how much of its rated writing life is used up. Free tools such as CrystalDiskInfo on Windows, smartctl on Mac and Linux, or the maker's own app can read the logbook and turn it into Good, Caution or Bad.

A few numbers matter most. Reallocated, pending or uncorrectable sectors that keep going up mean the drive is running out of good spots, so copy your files off soon. A rising CRC error count usually points at the cable or port, not the drive itself. SSD wear (Percentage Used, or Wear Levelling Count) shows how much of the drive's writing life has gone. A clean report is reassuring but not a promise: drives can still fail suddenly, which is why backups matter more than any health check. Many USB sticks, memory cards and cheap USB enclosures don't pass SMART through at all.

See it in action

  1. BonusIs my hard drive getting old? Reading its health chartTake Grandpa Spinner (a spinning hard drive) and Granny Chip (an SSD) for a check-up: change the readings on their SMART health chart, patched spots, wobbly spots, a crackly cable, temperature, age, writing life and spare pages, and hear what they tell you, from fit as a fiddle to stop using it now.8 min · interactive
  2. BonusWhy is copying to a USB stick so slow?Send ants carrying crumbs from a laptop, over a bridge, into a USB stick and watch what really slows a copy down: a skinny USB 2 bridge, tired ants when the fast cache runs out, or paperwork for thousands of tiny files.10 min · interactive
  3. 8Where do deleted files and photos go?Delete a photo, empty the bin, and watch what really happens on a pretend disk: the file is forgotten, not rubbed out.7 min · interactive

Do it for real

Free grown-up tools and guides on Tooltern, our sister site. They work in your browser and nothing is uploaded.

Related words

  • SLC cache A small, fast part of a USB stick's or SSD's memory that new data is written to first, so copies start quickly and slow down once it fills.
  • Partition table (MBR vs GPT) The small map at the start of a drive that says where each section begins; MBR is the old kind many cars and TVs need, GPT the newer one computers use.
  • Journaling When a file system writes a quick note of what it's about to change before changing it, so it can tidy up after a sudden power cut.

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