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Unless you encounter a firmware bug that causes premature death of a drive, the wearout of a SSD is pretty predictable and is based on the volume of data writte

Unless you encounter a firmware bug that causes premature death of a drive, the wearout of a SSD is pretty predictable and is based on the volume of data written rather than time elapsed. NAND flash memory has limited write endurance, and that can be measured by testing individual dies far more quickly than testing an entire SSD to death. Based on known program/erase cycle limits for the NAND they're using, SSD manufacturers can make pretty accurate projections for how long (in TB written) the drive as a whole can survive, accounting for how that drive's controller manages the flash and what kind of write amplification can be expected from the intended workloads. The most significant limitation where manufacturers have to go out on a limb with their projections pertains to the standard requirement that a consumer SSD needs to be able to retain its data in a read-only state for a year after reaching the end of its rated write endurance. NAND manufacturers can very quickly bring flash to that level of wear, but they can't wait a year to measure retention characteristics before shipping. So they make projections based on high-temperature accelerated testing.

867-5309 6y ago
so if you use the 500GB drive and download e.g. 1TB of torrents per day, the write endurance predicts your drive will last less than a year, on average
- GordonS 6y ago
  Seems like an odd thing to say - how are you going to download 1TB/day on a drive that can hold only half that in total?
  - 867-5309 6y ago
    perhaps as an intermediary with a NAS endpoint? it was just an example, like 1.5 years for the 1TB version or 3 years for the 2TB, you get the idea
mgerdts 6y ago
The performance is also impacted by the write pattern. Drives endurance numbers are for 4 KB random writes on a drive that was preconditioned with 1 or 2 full overwrites. The only workload that is worse is 512 byte random writes (I think). This workload causes a lot of garbage collection (compacting 4 KB pages into e.g. 1 MB blocks) to allow blocks to be erased so that new pages can be written. This contributes to more program/erase cycles than you would expect ("write amplification factor"). Increasing over-provisioning, as I suggested in another comment, allows garbage collection to run less frequently and reduces the write amplification factor. Sequential large writes will also reduce write amplification factor. Rewriting blocks that are only in DRAM cache or dynamic SLC will also reduce wear.

867-5309 6y ago

so if you use the 500GB drive and download e.g. 1TB of torrents per day, the write endurance predicts your drive will last less than a year, on average

GordonS 6y ago
Seems like an odd thing to say - how are you going to download 1TB/day on a drive that can hold only half that in total?
- 867-5309 6y ago
  perhaps as an intermediary with a NAS endpoint? it was just an example, like 1.5 years for the 1TB version or 3 years for the 2TB, you get the idea

mgerdts 6y ago

The performance is also impacted by the write pattern. Drives endurance numbers are for 4 KB random writes on a drive that was preconditioned with 1 or 2 full overwrites. The only workload that is worse is 512 byte random writes (I think). This workload causes a lot of garbage collection (compacting 4 KB pages into e.g. 1 MB blocks) to allow blocks to be erased so that new pages can be written. This contributes to more program/erase cycles than you would expect ("write amplification factor"). Increasing over-provisioning, as I suggested in another comment, allows garbage collection to run less frequently and reduces the write amplification factor. Sequential large writes will also reduce write amplification factor. Rewriting blocks that are only in DRAM cache or dynamic SLC will also reduce wear.