You don’t have to wait for a hard drive to fail to find out it’s in trouble. A few minutes with the right checks can tell you whether a drive is healthy, quietly degrading, or on the edge — giving you the chance to back up before it’s too late. Here’s how to read a drive’s health, and what the warning signs actually mean.
Every drive keeps a health log called SMART. Reading it — free, in minutes — reveals reallocated and pending sectors, the clearest early signs a hard drive is starting to fail.
Every modern hard drive continuously monitors itself through a system called SMART (Self-Monitoring, Analysis and Reporting Technology), logging dozens of internal figures. You can read it for free: on Windows, CrystalDiskInfo gives a clear “Good / Caution / Bad” verdict; on a Mac, tools like DriveDx or the smartmontools package do the same; many drive makers offer their own utilities too.
An overall status of anything other than “Good” is a serious flag. But the individual figures tell the real story, which is where to look next.
Among all the SMART attributes, a few are the ones that count. Watch these:
Bad sectors the drive has swapped out for spares. A few can be normal; a rising count means the surface is degrading.
Sectors the drive suspects are bad and is waiting to reallocate. Any pending sectors are a warning.
Sectors the drive couldn’t read or fix at all. These directly threaten data and shouldn’t be ignored.
How often the drive struggled to spin up. Rising values point to a tiring motor.
Beyond SMART, the operating system can check the drive’s file system for problems. On Windows, CHKDSK (right-click the drive → Properties → Tools → Check, or chkdsk /f) scans for and fixes logical errors; on a Mac, Disk Utility’s First Aid does the equivalent. This won’t fix a physically failing drive, but it catches file-system corruption early.
One caution: don’t run repeated repair scans on a drive you suspect is physically failing — if it’s making noises or throwing read errors, scanning keeps it working hard and can make things worse.
Software isn’t the only diagnostic. A healthy hard drive is quiet and steady; new noises — clicking, grinding, a repetitive buzz — are among the clearest signs of mechanical trouble, and they mean stop, not scan. Watch performance, too: a drive that’s become slow, freezes when opening files, or stalls mid-copy is often struggling with bad sectors.
Trust these signs even if SMART looks clean — drives can fail mechanically with a healthy-looking log right up to the end.
Put it together like this. Good SMART, quiet, fast, no errors — the drive is healthy; keep backing up as normal. A few stable reallocated sectors but otherwise fine — keep an eye on it and make sure your backups are current. Rising bad sectors, a “Caution” status, slowdowns, or any noise — treat the drive as failing.
“Failing” doesn’t mean panic, but it does mean act: back up your important files now and plan to replace the drive, before a warning becomes a failure.
If the checks point to a failing drive but it’s still readable, back up immediately — most important files first — then replace it. Don’t keep trusting a warning drive, even if it seems to be behaving; SMART flags and bad sectors only trend one way.
If it’s already making noises or dropping out, stop using it and don’t run more scans — that’s a hardware fault, and a diagnostic will tell you what’s recoverable without risking further damage.
What people ask us most about checking drive health.
Read its SMART data with a free tool — CrystalDiskInfo on Windows, DriveDx or smartmontools on a Mac — and look at the overall status plus key figures like reallocated and pending sectors. Run a CHKDSK or Disk Utility scan for file-system errors, and listen for noises and watch for slowdowns. Together these give a reliable picture in a few minutes.
The clearest warnings are a rising Reallocated Sectors Count, any Current Pending Sectors, and Uncorrectable Sector errors — these indicate the drive’s surface is degrading. A Spin Retry Count that’s climbing points to motor trouble. An overall SMART status of “Caution” or “Bad” should be treated seriously: back up now and plan to replace the drive.
Yes. SMART and error scans catch gradual, surface-level decline well, but drives can fail suddenly from mechanical or electronic faults with a clean report right up to the moment they go. If you have any physical symptoms — noises, freezes, disappearing files — trust those over a passing check, and always keep a current backup regardless.
If SMART is flagging or the drive is slowing down, back up while you still can. If it’s making noises or dropping out, stop and send it in for a free diagnostic. Post it in from anywhere in the UK, or drop it to us in Belfast.