You don’t need to wait for a hard drive to fail to know it’s in trouble — the drive keeps its own health data, and a few built-in tools will show it to you in minutes. Here’s how to check a hard drive’s health on Windows and Mac, which readings to trust, and how to tell when a result means it’s time to back up and stop.
Every modern drive monitors itself through SMART. Free and built-in tools read those figures, so you can see reallocated sectors, pending errors and overall status — and get warned before a drive fails outright.
Hard drives (and SSDs) run a self-monitoring system called SMART — Self-Monitoring, Analysis and Reporting Technology. It tracks dozens of internal attributes, but a handful tell you almost everything: the reallocated sector count (bad spots the drive has already swapped out for spares), the pending sector count (suspect spots waiting to be dealt with), and the overall pass/fail status. A brand-new drive shows zeros; a healthy older drive shows low, stable numbers. Numbers that are high, or climbing each time you check, mean the drive is deteriorating — and that’s the single most useful thing a health check tells you.
On Windows, the quickest read comes from a free tool: CrystalDiskInfo shows each drive’s health status (Good, Caution or Bad) and lists the SMART attributes in plain terms, so you can see the reallocated and pending sector counts directly. For a quick built-in check, open Command Prompt and run wmic diskdrive get status, which reports “OK” or a warning per drive. To scan the file system and surface for errors, chkdsk (or right-click the drive → Properties → Tools → Check) will flag and mark bad sectors — though on a drive you already suspect is failing, run it only after your data is backed up, since a full scan works the drive hard.
On a Mac, the built-in starting point is Disk Utility → First Aid, which checks and repairs the drive’s file-system structure. For the underlying SMART status, open the Apple menu → About This Mac → System Report → Storage, where the drive’s SMART status shows as “Verified” or “Failing”. For the same detailed attributes Windows users get, the free command-line tool smartctl (part of smartmontools) reads reallocated and pending sector counts on a Mac too. As on Windows, First Aid is safe to run, but if the drive is noisy or clearly struggling, get the data off before repairing.
Interpreting a check is simpler than it looks. An overall status of Good/OK/Verified with zero or low, unchanging reallocated and pending sectors means the drive is healthy — check again in a few months. Any reallocated or pending sectors that are present and, worse, growing between checks mean the drive is failing slowly: back up now and plan to replace it. A status of Caution, Bad or Failing means act today. And remember the limits — SMART sometimes passes a drive that then fails, so if a drive is clicking, slow, or losing files, trust the symptoms over a clean result. If a drive has already failed, a hard-drive recovery is from £300 +VAT.
The quickest way is a free tool like CrystalDiskInfo, which shows a Good, Caution or Bad status plus the SMART attributes that matter, mainly reallocated and pending sector counts. For a built-in check, run wmic diskdrive get status in Command Prompt, and use chkdsk to scan for file-system and surface errors, though only after backing up if you already suspect the drive.
Start with Disk Utility and run First Aid to check and repair the file system. For the drive SMART status, go to the Apple menu, About This Mac, System Report, then Storage, where it shows as Verified or Failing. For detailed SMART attributes like reallocated sectors, the free smartctl command-line tool works on macOS.
A healthy drive shows an overall status of Good, OK or Verified, with zero or low and unchanging reallocated and pending sector counts. New drives read all zeros. The warning sign is not a single number but a trend, sectors that are present and climbing each time you check mean the drive is degrading, even if the overall status still says OK.
Yes. SMART is useful but not infallible, and drives sometimes fail with a clean SMART status, particularly from sudden mechanical or electronic faults. So a healthy reading is reassuring but not a guarantee, if a drive is clicking, running slowly or losing files, believe those symptoms and back up regardless of what SMART reports.
On a healthy drive, yes, CHKDSK is a normal maintenance tool. On a drive you already suspect is failing, it is safer to back up first, because a full scan makes the drive work hard for a long time and can worsen a physical fault or overwrite recoverable data. If the drive is noisy or clearly struggling, get it diagnosed rather than scanning it.
If a check shows growing bad sectors, a Caution status, or the drive is already misbehaving, don’t wait for it to fail. Send it in and we’ll tell you what’s recoverable — free diagnostic, fixed quote first.