Pourquoi ma vitesse de transfert de donnees USB fluctue-t-elle comme des montagnes russes ?
This is normal, it’s copying to a cache which is a lot faster than the storage on the drive, then when the cache is full the transfer speed drops because it can’t use the cache when it’s full. Then when the data has been written to the drive the cache is emptied and it can use the cache again, so you see a spike in the transfer speed.
The cache is used to speed up the transfer process, when the copy dialog closes it is still likely copying from the cache. It’s why on Windows we have “Safely Remove Hardware”, because it tells Windows to finish any remaining cached writes and then eject the disk so you can physically remove it.
You can disable write caching for the drive, search for “disable write caching for external drives in Windows” for the instructions. With write caching disabled on the drive, you can physically remove it as soon as the file transfer dialog closes instead of needing to wait until the write is finished.