I am running Ubuntu 18.04 on an HP Spectre which has USB-C connectors. I have a Samsung T3 500G SSD which I wipe & then rewrite to back up my data from the SSD of the HP. Transfer speeds for sequential transfer for the T3 are quoted as over 400 Mb/s. However my transfer speed (non-sequential) is around 40 Mb/s. What causes the slowdown ?