Why is my macbook pro ssd speed dropping?

Question

macOS

Decreasing speed of ssd on macbook 13 2012 ay7 8gb RAM. ssd kingston a400 240gb. 350/500 mb.s
The bottom line - in the blackmagic disk speed test on the first cycle, the speed is declared, the next cycle speed drops to ~ 150 for writing ~ 380 reading, sometimes the next cycle shows ~ 250 for writing, then again for 150 writing. Generally where to drip?
Applications run pretty quickly and everything suits, but knowing that the speed is not maximum, it's annoying. The disc is new, about 2 months old. There are no errors on the disk, trim is on, and so on. Sata3 connection, instead of the old hdd.

Answer 1

The bottom line is that in the blackmagic disk speed test on the first cycle, the speed declared

This is fine.
I have a speed limit of 180 km/h on my car.
And yet when I look at the speedometer it usually reads 40-90km/h.

but knowing that the speed is not maximum, annoying

If the speedometer of the car is up to 180, and you are driving around the city 40, does it bother you? Always prefer to keep the speed at the maximum?

Answer 2

There, rather, the SLC cache memory provides a fast write, but then it ends and starts writing to the memory itself and already more slowly (Here you can read more https://zen.yandex.ru/media/id/5b24f1e5b5b89100a8b...
Or as an option overheating, and as a result, a drop in speed