SSD health percentage explained: Percentage Used, Available Spare and TBW
Your SSD says 93% health, or Percentage Used 7%. Here's what's being counted and when to care.
The readings that matter
| Reading | Where you see it | Healthy | Worry when |
|---|---|---|---|
| Percentage Used | NVMe (smartctl, CrystalDiskInfo 05, Windows' Drive health) | Low and rising slowly | Near or past 100%: plan a replacement, keep backups |
| Available Spare | NVMe | 100% | Dropping, and urgent below the threshold |
| Media and Data Integrity Errors | NVMe | 0 | Any: back up today |
| Critical Warning | NVMe | 0x00 | Anything else (0x08 means it has gone read-only) |
| SSD Life Left (231), Wear Leveling Count (177), Media Wearout (233) | SATA SSDs, by maker | Normalised value near 100 | Below about 10 |
| Reallocated / runtime bad blocks (5, 183) | SATA SSDs | 0 or tiny | Growing |
How long will it last?
Divide the rated TBW by how much you write a year. A 1 TB drive rated for 600 TBW that you write 10 TB a year to (heavy for home use) has about 60 years of rated wear. Check your own rate from Data Units Written (smartctl shows it in TB) or CrystalDiskInfo's Host Writes, divided by the drive's age. Wear is rarely what kills a home SSD; controller faults and power problems are more common, and they don't show up in the percentage. That's why backups matter more than the number.
What happens at 100%
Nothing dramatic. 100% means you've reached the maker's rating, not that the flash has stopped. Endurance tests have run consumer SSDs to several times their rating. Near the true end, many drives switch to read-only so you can still copy files off, which the Critical Warning shows as 0x08.
Things that look scary but aren't
- Unsafe Shutdowns in the hundreds: normal on laptops and PCs that get switched off at the wall.
- Error Information Log Entries: often just commands the drive didn't support (sent by monitoring tools). Not a health reading on its own.
- A temperature of 50-65 °C under load is normal for NVMe. Over about 70 °C it may slow itself down; a heatsink helps.
The Wirebook drive check-up lesson draws this as Granny Chip's pencil notebook: each page wears a little every time you rub it out, and she has spare pages tucked in the back.
Related
Why an SSD benchmarks slow · Clone a hard drive to an SSD · How to check drive health · Reallocated and pending sectors · "This device can perform faster"
Questions
Is 90% SSD health good?
Yes. It means about 10% of the rated write endurance is used. At typical home use that often takes years, and the drive keeps working past 0% health too.
What does Available Spare mean?
The share of spare flash blocks still unused. Healthy drives show 100%. If it falls toward the threshold (usually 10%) the drive is replacing a lot of failing blocks, which is a real warning.
Does an SSD stop working at 100% Percentage Used?
No. It means the maker's rated write life is used up. Most drives carry on well beyond it, but back up and plan a replacement.
Why does CrystalDiskInfo show a different health than Windows?
They read the same counters but round or combine them differently, and SATA SSDs use maker-specific attributes. Look at the raw readings rather than the headline.
Published 路 updated .