Jack, I’ve edited my previous post and adding some info here: this pendrive is UMM3, not Mimic.
Goodram has changed the pendrives some time ago and I have both Mimic and UMM3 which should be the same, but aren’t. They downgraded the speed of RW and UMM3 (newer) is limited, where Mimic (older) shouldn’t be.
I will test Mimic now for the speeds and if sth unusual occurs, I will let you know.
Seems like all Goodram pendrives have low speeds so they are not applicable here.
I’ve tested them on Windows and speeds are R45/W24 MB/s.
I’ve tested also SanDisk Extreme U100 USB 3.0 32GB and it is getting these write speeds:
87.7, 81.6 and 89.5 MB/s.
On Windows this pendrive gets R227/W115 MB/s.
So it is pendrives issue, not Rock Pi related hardware/software/kernel.
Still good microSD does not achieve nominal speeds (max 16.3 MB/s).