Just a heads up for anyone using USB3 external SSD/HD on Raspberry pi4.
There are multiple reports of issues with poor performance and/or errors when using an USB 3 connected SDD/HD using various USB 3 to sata converters and also external USB 3 hard disks.
I have experienced such problems with my Pi 4 (4GB) with various USB 3 to sata converters with both 2.5 SSD and 2.5 hard disks.
Even if there are no errors being reported in dmesg, performance can be like USB 2 or worse.
There is a work round which downgrades from uas see https://www.raspberrypi.org/forums/view ... 8&t=245931
The work round gives reasonable performance, but not the best as uas is disabled.
I don't believe it is the whole story as the same setup on my Xubuntu 18.04 (kernel 4.18.0-25) laptop USB 3 port has excellent performance, as does another system running Debian Buster (kernel 4.19.0-5).
A quick test with the drive mounted, depending on how drive is mounted you might need sudo in front of the command.
dd if=/dev/zero of=test1 bs=4k count=2000k conv=fsync status=progress
This writes a 8GB file with all zeroes.
After the file has been written check using dmesg for errors.