If a 1TB SSD is rated at 600TB of guaranteed writes (TBW), burning through that rating before the five-year warranty expires takes 329GB of writing every single day. A PC used for documents, browsing and ordinary gaming writes roughly one hundredth of that, which would take more than eighty years to reach 600TB. On a consumer drive, the clock almost always runs out before the write budget does.
The reason to check TBW anyway sits in the warranty wording itself. Samsung's limited SSD warranty states that coverage ends at the stated period or the TBW threshold, whichever comes first. For video editing scratch disks or virtual machine logs moving hundreds of gigabytes a day, that order flips.
What the number actually guarantees
Samsung Semiconductor's tech blog defines TBW as the volume a drive can record over a given period, illustrating it with 100GB a day for ten years — 100 × 365 × 10 = 365,000GB, or 365TBW. Plain multiplication.
What matters is that this marks the end of coverage, not the moment of failure. Crossing TBW does not stop the drive that day, and a controller fault can kill a drive that has barely written anything. TBW is closer to a contractual line: the manufacturer stands behind the drive up to this much writing.
It also behaves differently from a battery cycle rating. A battery loses usable capacity as cycles accumulate; an SSD keeps its labeled capacity as long as spare blocks remain. Placing the two notations side by side, as in the piece on the 800-cycle 80% battery spec, makes the difference clear.
Double the capacity, double the TBW — and identical DWPD
Across Samsung's 870 EVO, 980 PRO and 990 PRO, TBW scales exactly with capacity. Convert it into a daily write allowance and DWPD — how many times a day the whole drive can be overwritten — and the ladder flattens. Values below are computed on a five-year, 1,825-day basis.
| Capacity | Rated TBW (TB) | Daily allowance (GB) | DWPD |
|---|---|---|---|
| 250GB | 150 | 82 | 0.33 |
| 500GB | 300 | 164 | 0.33 |
| 1TB | 600 | 329 | 0.33 |
| 2TB | 1,200 | 658 | 0.33 |
| 4TB | 2,400 | 1,315 | 0.33 |
The right-hand column never moves off 0.33. Buying more capacity buys more absolute write headroom, but the number of times you can rewrite the drive is the same at 250GB and at 4TB. "Bigger lasts longer" holds only on the first measure. Fill a 4TB drive every day and it burns its warranty at exactly the rate a 250GB drive would.
At 20GB a day, how many years?
Using a 1TB, 600TBW drive: 600TB is 600,000GB, so the number of days equals 600,000 divided by the daily write volume.
| Daily writes (GB) | Days to exhaust | Years | Versus 5-year term |
|---|---|---|---|
| 10 | 60,000 | 164.4 | term ends first |
| 20 | 30,000 | 82.2 | term ends first |
| 50 | 12,000 | 32.9 | term ends first |
| 100 | 6,000 | 16.4 | term ends first |
| 200 | 3,000 | 8.2 | term ends first |
| 329 | 1,825 | 5.0 | exact break-even |
| 500 | 1,200 | 3.3 | TBW ends first |
| 1,000 | 600 | 1.6 | TBW ends first |
Break-even is 329GB a day. Counting concrete workloads against that line makes the decision easy: re-downloading one 100GB game daily is 100GB, and 4K project scratch files running 200–300GB a day reach the line on their own. Documents, browsing and occasional installs rarely clear 20GB.
TBW answers "when does coverage end," not "when does it break." On a home PC, the line that gets crossed first is almost always the five years.
Why rival brands print the same figure
Line up published manufacturer specs and TBW stops looking like a quality ranking. The per-capacity endurance StorageReview lists for the WD_BLACK SN850X matches Samsung's 990 PRO exactly.
| Capacity | Samsung 990 PRO (TB) | WD_BLACK SN850X (TB) | Warranty |
|---|---|---|---|
| 1TB | 600 | 600 | 5 years, both |
| 2TB | 1,200 | 1,200 | 5 years, both |
| 4TB | 2,400 | 2,400 | 5 years, both |
Neither copied the other; consumer TLC warranty policy has simply converged on the same 0.33 DWPD convention. Comparing TBW alone therefore tells you little. With the figures tied, the real separation happens in controller thermals, post-SLC-cache write speed and random performance — territory covered in the piece on when Gen5 speed stops being noticeable.
Where 0.33 comes from
Digital Post puts NAND program/erase endurance at roughly 100,000 cycles for SLC, 3,000 for MLC and 1,000 for TLC. On TLC, which nearly every consumer NVMe drive uses, a 1TB drive's theoretical write total is 1,000 cycles × 1TB = 1,000TB.
A 600TB rating is 60% of that. The missing 40% is the point. The controller spreads writes across all cells through wear leveling, which means more data reaches the NAND than the host requested. Add spare area reserved for failing blocks and the manufacturer's safety margin, and the guaranteed figure lands well below the theoretical one.
End-of-life behavior also varies. The same article notes that some models switch to a read-only mode at end of life, leaving stored data retrievable. Losing detection outright and being left with a read-only volume are very different recovery problems.
Checking how much you have already written
Samsung's tech blog points to its Magician utility, which reports drive health in three states. Without a vendor tool, the standard NVMe SMART fields do the job: Data Units Written, Percentage Used and Available Spare.
The math is one division. Cumulative writes divided by rated TBW gives the consumption ratio; dividing that by elapsed years gives the annual burn rate. A two-year-old 1TB drive showing 40TB written is at 40 ÷ 600 = 6.7%, or 3.3% a year — which puts full exhaustion 28 years out at the current pace.
Who should size up, and who should not
Stepping up a capacity tier for endurance reasons makes sense when daily writes routinely exceed 100GB: 4K editing scratch space, a game library reinstalled constantly, virtual machine images and database logs. Moving to 2TB doubles the daily allowance to 658GB and halves the burn rate for the same workload.
For documents, browsing and ordinary gaming there is no endurance argument for buying larger. The real reason to size up there is free space, not lifespan. As a drive fills, the controller has fewer empty blocks for wear leveling and internal data movement rises for the same host writes. Leaving headroom does more for longevity than chasing a bigger TBW number.
Check before buying
- Whether the warranty text reads "period or TBW, whichever comes first" — a term-only figure has the condition omitted
- That TBW differs by capacity within the same model name; applying a reviewed 1TB figure to a 500GB drive doubles the estimate
- Your own daily write estimate in gigabytes — game reinstalls, editing caches, backup frequency — against the 329GB line for a 1TB drive
- Cumulative writes and percentage used on your current drive, the only measured basis for a replacement decision
- Whether the drive supports read-only fallback at end of life; if not, tighten the backup interval