This is actually better for most consumers. The SLC cache was increased nearly three fold and the controller is a superior one (it now uses the same one as the 980 PRO). TechPowerUp[0] has a much better post on this, and you can clearly see there that the new one is better in most cases than the old one.
The only ones disadvantaged by this change are people who constantly write >42GB which I would think are video editors. (The old version would get a speed reduction to 1500MB/s after overflowing the SLC cache (42GB), the new one goes down to 800MB/s after overflowing (115GB))
P.S.: Not defending this, just clarifying because most posters here seem to believe it's a straight up downgrade. Should also be worth noting that Samsung changed the product box, product number, firmware version and the spec sheet for this change. So they're significantly better than the others who have done similar moves. That said, I still believe that they should have called this the 971 Evo+ or something, as it's genuinely different.
> Should also be worth noting that Samsung changed the product box, product number, firmware version and the spec sheet for this change
This is yugely better than what some other SSD makers have done. ADATA for example has massively downgraded some drives, trying to sell those under the same name and part numbers as a popular good-selling drive, and done so completely silently. ADATA isn't the only one. The screaming about this situation is endless on several pc part enthusiast subreddits.
What Samsung should have done it change the name and call it the "971 Evo Plus SSD" or "970 Evo Gold SSD" or some such change that distinguishes this new product with different performance characteristics than the actual "970 Evo Plus SSD".
But no they want to benefit from the good name and customer perception of the "970 Evo Plus SSD" while selling a substantially different product under that name. That is fraudulent behavior!
How can they do that without reducing the overall capacity? My understanding is that part of the MLC storage in SSDs is used as an SLC cache so that it's faster, but can store only half, one third or one fourth of the data it otherwise would.
In general, there are two separate components to the SLC cache strategy (which as you said, is writing only one bit instead of 3 for TLC, because it's much faster to do so). First you have some overprovisionned NAND, the size of which depends with models. I believe it is 6 GB on this one.
Then you have what they call "intelligent turbowrite", which is a dynamically allocated/reallocated SLC cache (about 108 GB).
For both, the concept is broadly the same, your writes go into the overprovisionned "SLC cache" first, then into the dynamic one.
When the drive is idle, it will consolidate the writes of both caches as 3 bit writes, freeing the NAND for "SLC cache" use again. This can take a few minutes of idle time.
As you fill up your disk things get more complicated, you need to keep some free space to be able to consolidate your writes, the exact way this controller works in that case is not known to me, but this is an issue with every SSD that's not full SLC. Modern controllers usually are doing much better than the old ones.
Generally SLC cache has almost no connection to the overall size of the drive. After finishing writing a huge portion of data (for example), the controller will start to move the written data out of the SLC section and turn them into normal TLC mode, releasing the SLC space for next turn of writing. When the drive usage becomes higher, some drive (apparantly Samsung's drive does) have a dynamic SLC capacity policy that will reduce the avaliable SLC space, so the disk can have enough space to store normal TLC data.
Consumer SSDs don't have a a lot of overprovisioning. For example, a 1 TB SSD will never have more than 1 TiB of flash. Server SSDs are a different story.
> a 1 TB SSD will never have more than 1 TiB of flash
It's a bit more complicated than that. None of the quantities precisely correspond to the definitions of 1TB = 1000^4 or 1TiB = 1024^4 bytes. A "1TB" drive will have a host-accessible capacity of 1,024,209,543,168 bytes.
The NAND chips on a consumer 1TB drive will collectively have a nominal capacity of 1TiB (1,099,511,627,776), but that's more of a lower bound; the actual capacities those chips add up to will be higher. If we assume defect-free flash and count the bits used for ECC in order to get an idea of how many memory cells are physically present, then we get numbers as high as 1,335,416,061,952 bytes for our 1TB drive. If we don't count the space reserved for ECC, then we're down to about 1,182,592,401,408 bytes on defect-free flash, and 1,172,551,237,632 after initial defects (taken from a random consumer TLC drive in my collection).
So that means the SSD is starting out with about 14.48% more capacity to work with than it provides to the host system—considerably more than the 9.95% discrepancy between the official definitions of 1TB and 1TiB. Of course, that 14.48% will be reduced as the drive wears out, and the low-grade flash used in thumb drives and bargain barrel SSDs from non-reputable brands will tend to have more initial defects.
The only ones disadvantaged by this change are people who constantly write >42GB which I would think are video editors. (The old version would get a speed reduction to 1500MB/s after overflowing the SLC cache (42GB), the new one goes down to 800MB/s after overflowing (115GB))
P.S.: Not defending this, just clarifying because most posters here seem to believe it's a straight up downgrade. Should also be worth noting that Samsung changed the product box, product number, firmware version and the spec sheet for this change. So they're significantly better than the others who have done similar moves. That said, I still believe that they should have called this the 971 Evo+ or something, as it's genuinely different.
[0]: https://www.techpowerup.com/286008/et-tu-samsung-samsung-too...