Why does my write/read speed go down?

[gr8pics]

I got a imac 27 late 2015, got a 2TB fusion drive, 1.5TB free space.
Using Disk speed test, loading file 5gb, and runs continously, it shows 600/1500 once or twice, but 9 out of 10 times it slows down to 160/160
Can someone explain why?Im running the test from the root of user folder.

OSX 10.12.4

 

[keysofanxiety]

I can only imagine it's running from the HDD when it shows the slower speeds. Fusion drives merge both the HDD and SSD into a logical volume, swapping between the two through under-the-hood algorithms, so running from the root of the user folder wouldn't necessarily mean it's testing from the SSD.

Regardless, the best benchmark is whether you're seeing an impact in your workflow. If it's running just as smoothly as before, there shouldn't be a cause for concern.

 

[gr8pics]

I guess youre right, but i feel it affects the performance, especially when copying files, i guess its just under optimal conditions we can take advantage of full speed then...