Performance of copying large files

[cihe13375]

I tested the performance of an ext4 partition with crystaldiskmark, and the sequential write speed looks pretty good (the available system memory during testing is << 32GB): However, when actually trying to copy large files to the partition, I never get an average speed of over 300M/s. I tried file explorer default copy, robocopy, fastcopy (including trying various IO units, overlapping IO counts, using OS buffer or not, same or different drive mode, running as admin or not), but all results in similar slow speeds.

I'm wondering what is the reason of this difference, and if there is anything I can do to improve the performance of copy.

Note1: all partitions appearing above are on a Samsung 980 Pro 2TB drive. The partition D: is in ntfs and Y: is in ext4. Note2: I tried other disk benchmark softwares. Atto disk benchmark gives similar results as crystaldiskmark, but AS SSD benchmark gives very low write speeds, similar to what observed in real copying. Also it throws an error at the end of test, which does not appear when testing on an ntfs partition. Also the writing speed is normal (~3G/s) when testing on an ntfs partition.