S.M.A.R.T.: How a Drive Reports Its Own Health, Which Indicators Really Signal Imminent Failure, Why a "Good" Status Doesn't Guarantee Reliability and When It's Time to Copy Your Data Urgently

Almost every hard drive and SSD made in the last twenty years keeps an internal log of its own health. The technology is called S.M.A.R.T. — Self-Monitoring, Analysis and Reporting Technology. The drive counts read errors, relocated damaged areas, power-on hours, temperature and the number of start-ups, and an SSD also tracks how worn its memory cells are. Sometimes a computer shows a warning at start-up — "S.M.A.R.T. status bad, backup and replace" — but more often the problems are only visible to someone who deliberately looks at these indicators. Let's look at what they mean and how to use them so you don't lose data.

The key indicators for a hard drive

• Reallocated Sectors. When a drive finds a damaged area of the surface, it moves the data to a spare zone. A few reallocations happen even on healthy drives, but if the number grows week by week, the surface is degrading.
• Current Pending Sectors. Areas the drive couldn't read and is waiting to reallocate. This is one of the most alarming signs: data in those spots may already be inaccessible.
• Uncorrectable errors (Offline Uncorrectable, Reported Uncorrectable). Errors the drive couldn't fix even with its built-in correction.
• Interface errors (UDMA CRC Errors). These usually point not to the drive surface but to a bad cable or connector. They're still worth fixing, because they cause freezes and data corruption during writes.
• Spin-up time and retries. Rising values can indicate mechanical or power problems.

The key indicators for an SSD

• Wear or remaining life. Flash memory cells withstand a limited number of rewrites. The SSD shows the percentage of its life used, or the amount of data written relative to its warranty rating.
• Spare blocks. The number of reserve blocks for replacing worn ones. When the reserve runs out, the SSD may switch to read-only mode or fail.
• Media and data integrity errors. Their appearance on an SSD is a serious warning.
• Temperature. Especially important for fast NVMe drives in laptops, which throttle when they overheat.

What S.M.A.R.T. can and can't do

S.M.A.R.T. is good at warning of gradual degradation: a growing number of bad sectors, SSD wear, cable problems. But many failures happen suddenly with no warning at all: electronics killed by a power surge, heads damaged by a knock, an SSD controller failing. Studies by large data centres show that a significant share of drives die without showing any alarming values beforehand. So a "good" S.M.A.R.T. status is no reason to skip backups, while a "bad" one is a reason to make a copy immediately.

Why you shouldn't trust the overall rating alone

The built-in overall rating of "OK" or "Good" only changes when a parameter crosses a threshold set by the manufacturer. Those thresholds are often very lenient: a drive with hundreds of pending sectors can still be considered "healthy". It's more important to look at the specific indicators and how they change over time than at the summary status.

Monitoring

For home computers, checking drive health with a dedicated program from time to time is enough. In offices, on servers and network storage, it's worth setting up automatic monitoring with alerts to a responsible person: many NAS devices do this themselves once you enter an email address. Then you'll learn about a problem sector the same day, not after the server stops booting.

When it's time to act

• Pending or uncorrectable sectors have appeared — copy important data urgently and plan a replacement.
• The number of reallocated sectors is growing — replace the drive soon.
• The SSD's life is nearly used up — prepare a replacement.
• The computer shows a S.M.A.R.T. warning at start-up — make a copy immediately, without delay.
• The drive has become slow, freezes or makes new noises — check its condition even if S.M.A.R.T. is silent.

What our technician does

1. Reads and interprets the S.M.A.R.T. data of every drive in a computer, server or NAS.
2. Runs additional surface and speed tests if anything looks suspicious.
3. If there are warning signs, copies the data gently without loading the drive with unnecessary checks.
4. Replaces the drive and transfers the system and data.
5. Sets up monitoring and alerts, especially for office servers and NAS devices.

A real example

An accountant from Vashlijvari got in touch because her computer had started "thinking" when opening files. Windows' built-in check said the drive was fine. Our technician looked at the S.M.A.R.T. data: the hard drive had more than 200 pending sectors, and the number was rising with every start-up. We immediately imaged the drive on equipment that handles problem areas gently and saved all the data, including the accounting database. We then fitted an SSD, transferred the system and set up a weekly backup. A few days later, the old drive stopped being recognised altogether during testing.

Call a technician

If your computer has become slow, is showing a drive warning, or you want your drives' health checked, we'll come to any district of Tbilisi around the clock. Learn more on our computer diagnostics, hard drive recovery and SSD recovery pages.