Samsung 970 evo slow write

2018-07-19 17:16:42

Debian 10 (installed in uefi with gpt) with kernel 4.16. Disk is set to PCIe Gen 3.0 x4. Maximum disk write is about 700 MB/s and read is 3500 MB/s. Tested with gnome-disks and dd. Scheduler automatically set to none. Why write speed is so slow ? Even without samsung slc turbowrite it should be about 1200 MB/s

Samsung specification: read 3 500 MB/s; write: 2 500 MB/s

What can be done to improve it ?