Mount Point May Conceal Used Disk Space

The df command shows disk is out of space, but du shows free space
The parent file system is out of disk space
The df and du command output does not match

# /bin/df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda3              14G  3.2G  9.5G  25% /
udev                  2.0G  132K  2.0G   1% /dev
/dev/sda1             487M   31M  431M   7% /boot
/dev/sdc1            1004M 1004M     0 100% /exports/base
on11:/data/files      8.0G   81M  7.9G   1% /exports/base/files

In the example above, /exports/base is out of disk space. Several files have been copied to the mount point /exports/base/files, but when on11:/data/files is mounted to the /exports/base/files mount point, the files taking up disk space cannot be seen. The du -sh /export/base would show approximately 8Gb of free disk space, even though df -h shows /export/base is full.

Unmount file systems from the parent file system, and remove any files in the mount points. Do to following to free up disk space consumed in the mount point.

1. umount /exports/base/files
2. ls -l /exports/base/files (NOTE: This directory is a mount point and should be empty of any files or subdirectories.)
3. rm -rf /exports/base/files/*
4. mount /exports/base/files