HARDWARE
SSD healthReading SMART, wear and lifespan
SSD health is read from SMART attributes, chiefly the percentage of rated write endurance used (or remaining). A drive reporting, say, 98% health has used about 2% of its rated writes. Modern consumer SSDs are rated for hundreds of terabytes written (TBW), far more than typical use, so most are replaced long before wear becomes the limiting factor.
What "health" actually measures
An SSD's reported health is derived from SMART (Self-Monitoring, Analysis and Reporting Technology) data. The headline figure most tools show is based on write endurance: how much of the drive's rated lifetime writing has been used. NAND flash cells wear out after a finite number of program/erase cycles, so the controller tracks writes and estimates remaining life.
| Term | Meaning |
|---|---|
| Percentage Used | Share of rated endurance consumed (NVMe) |
| Wear Leveling Count / Media Wearout Indicator | SATA equivalents, often counting down from 100 |
| TBW (Terabytes Written) | Total writes the drive is rated for |
| DWPD | Drive Writes Per Day over the warranty period |
| Available Spare | Reserve blocks left to replace failed ones |
Putting the numbers in context
A 1 TB consumer drive rated at 600 TBW can absorb 600 terabytes of writes. Typical desktop use writes a few terabytes a year, so the endurance lasts far longer than the drive is likely to be in service. A health figure of 95–99% after a couple of years of normal use is expected.
Endurance is not the only failure mode, though. Controllers, DRAM and power circuitry can fail suddenly, at any health level. Health metrics are not a guarantee; keep backups.
Warning signs worth acting on
- Available Spare falling toward its threshold (NVMe) or reallocated sectors climbing (SATA).
- A raised Critical Warning flag.
- Files becoming unreadable, or the drive dropping out and reappearing.
- Boot failures such as inaccessible boot device or unexpected store exception that correlate with the drive.
Any of these is a stronger replacement signal than the summary percentage.
Reading it
CrystalDiskInfo (Windows), the drive vendor's utility, or smartctl from smartmontools display the raw attributes. Note that health percentage and temperature are separate readings; a healthy drive can still throttle when hot. Running chkdsk checks the file system, not the drive's endurance.
Frequently asked questions
What does 98% SSD health mean?
It usually means about 2% of the drive's rated write endurance has been consumed, so 98% of the estimated write life remains. It is an estimate based on writes, not a countdown to failure, and it says nothing about sudden electronic failures, which can happen at any health level. Keep backups regardless.
How long do SSDs last?
For typical desktop and laptop use, well over the warranty period, often a decade or more, because everyday writing is far below the TBW rating. Heavy write workloads (video editing, databases, constant downloads) consume endurance faster. The controller and power electronics can fail independently of NAND wear.
What SMART values should I watch?
Percentage Used (or Wear Leveling Count / Media Wearout Indicator), Reallocated Sectors, Available Spare and Available Spare Threshold, and the Critical Warning flag on NVMe. A falling Available Spare or a raised Critical Warning is a stronger signal to replace than the headline health percentage.