XFS filesystem shows more space used in df than in du

Issue

• When running df -h, the XFS filesystem shows a certain amount of space used:

# df -h /boot
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdb1       496M  385M  112M  78% /boot

• But the output of the du -sh command shows a much lower number:

# du -sh /boot
134M    /boot

• There are no filesystems mounted under /boot, so there can not be any data hidden under another mountpoint.