I mount usb device like this:
sudo mount /dev/sdb1 /media/usb
and then copy a big file which about 1Gb to the device:
sudo cp ~/big_file /media/usb
Ordinary, if I copy a big file to usb, the command should run a few minutes. But it finish quickly.
And then I check the file in usb:
It is same as origin file. Then I umount the usb and it run a long time:
sudo umount /media/usb
When I remount the usb device and check the file with md5sum again, the file in usb is different from origin file.
I am sure the device is ok because I can copy the file success in Windows, so what is the problem of my system?