I recently purchased this 512gb USB 3.0 flash drive with advertised read speeds of up to 200mb/s and write speeds of up to 100mb/s. To use with my Mac with USB 3.0 ports. When I first used it, I transferred a large file (90gb) in about the advertised time: ~8 minutes. I tried this with the drive formatted in ExFat and HFS+ and got around the same speeds. I stuck with the ExFat formatting
But then I copied over a whole directory structure with many different folders and subfolders and, at some point, it started reading and writing extremely slowly. So now transferring the entirety of the files from the drive is being reported by MacOS as taking upwards of 17 hours, much more than what I would expect given that my 90gb file transferred so quickly. Occasionally, I'll get these random bursts of what seems like several gb in a period of seconds, but that happens rarely.
In addition, any kind of I/O operation seems to take an extremely long amount of time. Even merely loading 3 or 4 file icons in a directory can take upwards of 20 seconds. I've never encountered this before.
What's going on here? Could it be that the big directory structure and size of the drive mean that the filesystem has a lot of overhead involved with transferring the files? This seems normal, but in my case even trivial operations like loading a few file or directory icons from the drive take an extremely long time, longer than any other drive I've ever owned