Slow NVMe Write speed in Blackmagic on Samsung 970 EVO

[nervirasme]

Hey guys,

I'm having issues with write speeds of Samsung 970 EVO 250GB:

- When testing in Blackmagic with 1GB stress file - the speeds are fine! Screenshot:

- But when testing with 5GB stress file - the speeds start ok (same values as on 1GB stress), but after 2-3 seconds they drop significantly! Screenshot:

Anyone knows what the problem is?

If you need any other info:
- macOS version: Mojave 10.14.6
- Motherboard: Asus ROG Strix B360-I Gaming
- CPU: Intel i5-8500

Thanks!

 

[nervirasme]

Could it be something with the fact that my motherboard has only one PCIE slot and that they're all sharing the same bandwith? I have two M.2 drives connected (in their corresponding slots) and a RX570 GPU...

 

[jaymonkey]

@nervirasme,

Check the PCIe link speed of your NVMe in System Info/Profiler ..

For full speed you need x4, if it's running at x2 then it will run at half speed, initial high speed in test is most likely due to the I/O memory cache, once thats full it will step down to the direct read/write speed.

Cheers
Jay

 

[nervirasme]

@nervirasme,

Check the PCIe link speed of your NVMe in System Info/Profiler ..

For full speed you need x4, if it's running at x2 then it will run at half speed, initial high speed in test is most likely due to the I/O memory cache, once thats full it will step down to the direct read/write speed.

Cheers
Jay

I actually checked that before - it's already x4 :/

 

[gabevf]

@nervirasme same here, did you ever find out what was causing this?

I recently switched from APFS to HFS+J, and I wonder if that has something to do with it...