You’re also missing an important factor: Many drives now reserve some space that cannot be used by the consumer so they have extra space to work with. This is called factory overprovisioning.

> - Consumer drives like Samsung 980 Pro and WD SN 850 Black use TLC as SLC when about 30+% of the drive is erased. At this time you a burst write a bit less than 10% of the drive capacity at 5 GB/s. After that, it slows remarkably. If the filesystem doesn’t automatically trim free space, the drive will eventually be stuck in slow mode all the time.

This is true, but despite all of the controversy about this feature it’s hard to encounter this in practical consumer use patterns.

With the 980 Pro 1TB you can write 113GB before it slows down. (Source https://www.techpowerup.com/review/samsung-980-pro-1-tb-ssd/... ) So you need to be able to source that much data from another high speed SSD and then fill nearly 1/8th of the drive to encounter the slowdown. Even when it slows down you’re still writing at 1.5GB/sec. Also remember that the drive is factory overprovisioned so there is always some amount of space left to handle some of this burst writing.

For as much as this fact gets brought up, I doubt most consumers ever encounter this condition. Someone who is copying very large video files from one drive to another might encounter it on certain operations, but even in slow mode you’re filling the entire drive capacity in under 10 minutes.

> You’re also missing an important factor: Many drives now reserve some space that cannot be used by the consumer so they have extra space to work with. This is called factory overprovisioning.

This has always been the case, thus why even a decade ago the “pro” drives were odd sizes like 120g vs 128g.

Products like that still exist today and the problem tends to show up as drives age and that pool shrinks.

DWPD and TB written like modern consumer drives use are just different ways of communicating that contract.

FWIW I’d you do a drive wide discard and then only partition 90% of the drive you can dramatically improve the garbage collection slowdown on consumer drives.

In the world of ML and containers you can hit that if you say have fstrim scheduled once a week to avoid the cost of online discards.

I would rather have visibility into the size of the reserve space through smart, but I doubt that will happen.