[NAS326] Inconsistency in the used/free space

wdata

Hi, I have noticed about 1G is lost on one of my disk, and I out of ideas how to find it.
The df shows the 1.3T is used out of 2G disk (1.8G to be precise)
root@NAS326:/i-data/73edafc6# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_d2da5196-lv_73edafc6 1.8T 1.3T 580G 69% /i-data/73edafc6
However, the du only can find about 380G of it:
root@NAS326:/i-data/73edafc6# du -sh *
9.1M admin
12K aquota.user
16K lost+found
8.0K music
259G mymusic
16K nfs
8.0K photo
0 sysvol
34G tmp
8.0K video
70G webdav
root@NAS326:/i-data/73edafc6# du -sh .PKG
1.4G .PKG
root@NAS326:/i-data/73edafc6# su -sh .media
Unknown id: .media
root@NAS326:/i-data/73edafc6# du -sh .media
54M .media
root@NAS326:/i-data/73edafc6# du -sh .system
193M .system

Nothing in lost+found and nothing is mounted there (to be hidden under the mount point). Appreciate your ideas in finding that space.
Thank you!