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SSD health is not a single countdown number. For an NVMe drive, read the Critical Warning field first, then compare Available Spare with its threshold, treat Percentage Used as an endurance estimate, and compare composite temperature with the drive’s own warning and critical limits. Check media errors and whether counters are changing. If a critical warning, degraded reliability, or read-only state appears, back up important files immediately; do not wait for a life estimate to reach zero.
What an SSD health percentage actually tells you
Health labels in Windows and storage utilities summarize several SMART or NVMe health indicators. They are useful for spotting deterioration, but they are not guarantees and they do not predict an exact failure date. Intel notes that its remaining-life estimate is workload-dependent and can change when the workload changes. A drive that reports a favorable health percentage can still fail suddenly, while a drive whose endurance estimate has been consumed may continue operating.
For NVMe SSDs, the most useful evidence comes from the controller’s SMART/Health Information log. The fields describe spare capacity, estimated wear, temperature, data-integrity errors and operating history. Legacy SATA SSDs expose a different set of manufacturer-defined SMART attributes, so their raw values cannot be interpreted with one universal chart.
First identify the drive and interface
Record the exact model number before interpreting any value. Then establish whether the device is NVMe (usually connected through PCIe) or SATA. The distinction matters because the standardized NVMe fields discussed below do not map directly to every SATA attribute.
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- NVMe: look for fields such as Critical Warning, Available Spare, Percentage Used, Composite Temperature, Data Units Written and Media Errors.
- SATA: expect attributes such as reallocated sectors, wear-leveling count or percentage used, power-on hours and uncorrectable errors. Names and raw-value meanings vary by manufacturer.
Use the drive maker’s documentation for model-specific SATA attributes. A missing or unfamiliar attribute is not proof that the drive is healthy or unhealthy.
Check SSD health in Windows
Windows’ built-in NVMe view
- Open Settings.
- Choose System, then Storage.
- Open Advanced storage settings and select Disks & volumes.
- Select the disk you want to inspect and open Properties.
Labels and menu placement can differ between Windows releases. Microsoft’s documented storage-health feature monitors NVM (NVMe) SSDs; it does not provide the same health page for SATA SSDs or hard drives. If the page is absent, incomplete or limited to basic information, use a drive-compatible manufacturer utility or SMART tool rather than assuming anything about the drive’s condition.
Read the NVMe health fields in the right order
1. Critical Warning
Critical Warning is a bit field: more than one condition can be set at the same time. Relevant flags include:
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- Available spare has fallen below the drive’s Available Spare Threshold.
- Composite temperature is outside a warning or critical temperature threshold.
- Reliability has degraded.
- The medium has entered read-only mode.
- On devices that support it, volatile-memory backup has failed.
The field describes the controller’s current associated state; it is not a permanent log of every warning the drive has ever produced. A reliability-degraded or read-only condition deserves immediate attention. Microsoft explains that a read-only drive can still be read, but writes are unavailable. Copy important files to another device and follow the computer or drive maker’s support instructions before attempting repairs or firmware changes.
2. Available Spare and Available Spare Threshold
Available Spare is a normalized percentage of the SSD’s reserved replacement capacity. The threshold is the manufacturer-defined level at which the controller raises a low-spare warning. These values concern internal NAND spare capacity, not the amount of free space shown in File Explorer.
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For example, a disk can have hundreds of gigabytes free for files while its internal spare percentage has fallen below threshold. Conversely, a nearly full file system does not automatically mean that Available Spare is low. Interpret the two measurements separately.
3. Percentage Used and “remaining life” labels
NVMe’s standardized field is Percentage Used: the vendor’s estimate of the percentage of the NVM subsystem’s endurance that has been consumed, based on actual usage and the manufacturer’s prediction. Some utilities invert or rename this value and show an approximate “remaining life” percentage. Check the tool’s definition before treating the displayed number as equivalent.
A value of 100 means the estimated endurance has been consumed; it does not, by itself, establish that the SSD has failed. Values above 100 are permitted. The controller may update the estimate once per power-on hour while it is not asleep, so a change can appear without a large new workload.
This is not a calendar forecast. It cannot reliably tell you that a drive has six months or two years left. Workload, write amplification, temperature and the manufacturer’s endurance model all affect the estimate. Use it as a trend indicator and combine it with warnings and error counters.
4. Composite Temperature, WCTEMP and CCTEMP
NVMe Composite Temperature represents the controller and NVM subsystem as a combined reading. It may not equal the temperature at any one physical sensor. NVMe reports the value in kelvins; if a utility displays kelvins, subtract 273.15 to convert to Celsius.
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Each model supplies its own warning and critical thresholds:
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- WCTEMP: warning composite-temperature threshold.
- CCTEMP: critical composite-temperature threshold.
There is no single “normal SSD temperature” that applies to every model, enclosure and workload. Compare the current reading with that drive’s thresholds. The health log can also report accumulated minutes above the warning and critical thresholds when the device supplies those values. A brief peak is different from sustained operation above a threshold.
5. Data Units Written
Data Units Written is a host-write counter, not a remaining-life percentage. NVMe defines each reported unit as 1,000 512-byte units, with the count rounded up; metadata is excluded. Use the counter to understand workload and compare it with the endurance rating for that particular SSD. It cannot, by itself, produce a dependable failure date.
When comparing snapshots, record the date and the counter value. A rapidly increasing rate may explain a changing Percentage Used estimate and can reveal an unexpected write-heavy process, but it does not prove that the NAND is defective.
6. Media Errors and Error Information Log Entries
Media Errors counts detected unrecovered data-integrity errors. Error Information Log Entries counts entries recorded over the controller’s life. A nonzero historical value warrants investigation, especially if it increases or appears alongside a Critical Warning. A single static count is not a standalone failure forecast.
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7. Unsafe Shutdowns
Unsafe Shutdowns increments when power is lost without the required shutdown notification. Laptop battery depletion, forced resets and power interruptions can raise this number. It indicates power history rather than a direct NAND-wear percentage. Look for a pattern and investigate power, firmware or system stability if the count rises unexpectedly.
A repeatable reading sequence
- Identify the model and interface. Save the model, firmware version and whether it is NVMe or SATA.
- Read Critical Warning. Expand the field or decode its individual flags; record every active condition.
- Compare spare values. Check Available Spare against Available Spare Threshold, not against free capacity in the operating system.
- Interpret wear. Treat Percentage Used as a manufacturer-based endurance estimate, not as remaining years. If the utility says “life remaining,” verify whether it is simply an inverted Percentage Used value.
- Check temperature against the model’s limits. Note current Composite Temperature, WCTEMP, CCTEMP and any accumulated time above those limits.
- Review counters. Record Data Units Written, Media Errors, Error Information Log Entries and Unsafe Shutdowns. Recheck later to see which values change.
- Protect data when a warning appears. Back up important files promptly and consult the system or drive manufacturer. Do not wait for an estimate to reach zero.
How to interpret common result combinations
| What you see | What it means | What to do |
|---|---|---|
| Critical Warning clear; spare above threshold; no media errors | No NVMe warning is currently asserted. This is not a guarantee against sudden failure. | Keep normal backups and monitor trends. |
| Percentage Used at 100 or above; no other warning | The modeled endurance has been consumed or exceeded; the drive may still operate. | Confirm the model’s endurance specification, maintain backups and plan replacement based on workload and risk. |
| Available Spare below threshold | Reserved replacement capacity is low; this is unrelated to ordinary free space. | Back up important data and obtain manufacturer guidance. Prepare a compatible replacement. |
| Temperature above WCTEMP or CCTEMP | The composite reading has crossed a drive-specific warning or critical limit. | Improve cooling and airflow, reduce sustained load, and investigate whether the warning clears. Treat a persistent critical warning as urgent. |
| Reliability degraded or read-only mode | The controller reports a serious reliability state; writes may be blocked in read-only mode. | Copy data immediately while reads work, then follow support or replacement procedures. |
| Media Errors increasing | Unrecovered integrity errors are being detected. | Back up, check connections and firmware guidance, and plan replacement if the count continues to rise. |
| Only Unsafe Shutdowns increasing | Power-loss events are being recorded; this does not directly measure NAND wear. | Investigate power, battery, cable, reset and operating-system stability. |
Temperature troubleshooting
First verify that the utility is showing Celsius rather than kelvins and that you are reading Composite Temperature, not a different sensor. Compare the value with WCTEMP and CCTEMP for the exact model. If the drive is repeatedly near or above a threshold:
- Ensure the motherboard’s M.2 heatsink or thermal pad contacts the drive correctly and that any protective film was removed.
- Improve case airflow and remove dust from intake and exhaust paths.
- Check whether a sustained transfer, compilation, virtual machine or other write-heavy task is causing the rise.
- Update firmware only according to the manufacturer’s documented process and after securing a backup.
- Recheck both the current temperature and accumulated minutes above thresholds after cooling changes.
A lower idle number does not erase a recorded critical-temperature event. Conversely, a short workload peak below the model’s critical threshold is not evidence of a failing SSD.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.SATA SSDs need model-specific interpretation
Windows’ documented health page does not cover SATA SSDs or hard drives. SATA SMART attributes are defined and named by manufacturers, and the same attribute ID can have different raw-value meanings on different models. A “health percentage” from one vendor’s utility may be calculated differently from another’s.
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When to back up, replace or keep monitoring
Back up immediately
Back up important files as soon as a Critical Warning appears, reliability is degraded, the drive becomes read-only, Available Spare falls below threshold or Media Errors increase. Microsoft’s consumer guidance specifically recommends backing up when its critical storage warning appears. Verify that the backup can be opened; a second copy on a separate device is more useful than an untested copy.
Plan replacement
Replacement is justified by a persistent critical warning, worsening integrity errors, read-only behavior, repeated threshold temperatures that cannot be corrected, or a workload that has consumed the manufacturer’s endurance margin and carries high downtime risk. Choose a replacement only after checking the computer’s supported interface (SATA or NVMe), physical form factor, capacity, operating-system support and workload requirements. An unspecified computer cannot be matched to one exact replacement model.
Continue monitoring
If warnings are clear, spare capacity is above threshold, error counters remain stable and temperatures stay within the model’s limits, continue routine backups and periodic checks. Save dated readings so that you can distinguish a stable historical count from a newly worsening condition.
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- They are predictions. The manufacturer models endurance from usage and expected NAND behavior; actual workloads can differ.
- Workloads change. A drive used mostly for reads may wear differently after a database, video-cache or virtual-machine workload is introduced.
- Different tools use different labels. One utility may expose raw Percentage Used; another may display an inverted approximation.
- Endurance consumption is not an instant failure switch. Reaching 100 or more does not establish subsystem failure, while a sudden electronic or firmware fault can occur before that point.
Use the estimate to support planning, not to defer backups or promise a service-life date.
What the numbers cannot tell you
SMART and NVMe health data cannot guarantee that every file is readable, predict the exact hour of failure or establish a universal safe temperature. They also cannot turn a host-write counter into a precise remaining-years calculation without the specific SSD’s endurance specification and workload context. A clean snapshot is evidence of the current reported state, not a warranty.
For a serious warning, preserve data first. After the backup is verified, collect the model, firmware, warning flags and dated counter readings for the manufacturer or system maker’s support team.
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