I have two additional disks /dev/sdb1 and /dev/sdc1 which are mounted on "/home/user/xxx1" and "/home/user/xxx2". But I am surprisingly find that although the files use the space on their disk, they also use the space on my os disk /dev/sda1. So it seems they are using double space.
du -h give the following information:
/dev/sda1 16G 13G 2.6G 83% / /dev/sdc1 20G 3.7G 15G 20% /home/user/xxx2 /dev/sdb1 20G 5.0G 14G 27% /home/user/xxx1
but without xxx1 and xxx2, there are only a little files on the os disk.
It's really strange, is there anybody have any idea about this question?