Hi, when I check the cell's disk, it's using 10G but df result reports only 5G is used. Can I know why?

diego-cell/b3d42906-84f3-40db-8361-64232dac4ff8:/var/vcap/data# df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            3.9G  4.0K  3.9G   1% /dev
tmpfs           799M  548K  798M   1% /run
/dev/xvda1      2.9G  1.9G  866M  69% /
none            4.0K     0  4.0K   0% /sys/fs/cgroup
none            5.0M     0  5.0M   0% /run/lock
none            3.9G  3.6M  3.9G   1% /run/shm
none            100M     0  100M   0% /run/user
/dev/xvdb2       91G  5.1G   81G   6% /var/vcap/data

Regards,

Kyungwon Kang.