Copying Files to USB Flash Drives
Many people complain about corrupt files on USB flash drives.
USB flash drives are not the same as hard disks. These devices write and read slower. Linux systems use disk caching. Often disk caching creates an illusion of a file being written to a USB flash drive when actually that is not the case.
A good practice is to always use safe unmounting. That ensures the write operation is completed.
This is especially true with large files. Large files take a long time to copy to a USB stick, despite the desktop file manager dialog indicating the copy is finished. This can observed a little better by using a console based file manager such as midnight commander (mc). mc will not close the copy dialog until the operation completes.