NAS542 Raid6 4x6TB - Volume1 used capacity much larger than actually stored

In Storage Manager Volume1 shows as healthy with a capacity of 10.82 TB, of which 9.98 TB is used.

But a DU command shows that only 2.0 TB of data is stored in my file system,

/i-data/d895772b.

Where can the missing 8 TB be?

In CLI it looks like this:

BusyBox v1.19.4 (2021-04-01 13:06:33 CST) built-in shell (ash)
Enter 'help' for a list of built-in commands.

~ # df -h
Filesystem                Size      Used Available Use% Mounted on
...

...

/dev/md2                 10.8T     10.0T    863.3G  92% /i-data/d895772b
/dev/md2                 10.8T     10.0T    863.3G  92% /usr/local/apache/htdocs/desktop,/pkg
~ # du -c -s -d 1 -h /i-data/d895772b
20.0G   /i-data/d895772b/admin
357.6G  /i-data/d895772b/TM2020
13.9M   /i-data/d895772b/.PKG
610.3G  /i-data/d895772b/Backup
26.5M   /i-data/d895772b/.media
4.3G    /i-data/d895772b/Lydbøker
16.0K   /i-data/d895772b/lost+found
92.1M   /i-data/d895772b/.system
4.0K    /i-data/d895772b/Randi
61.1G   /i-data/d895772b/photo
2.3G    /i-data/d895772b/music
874.7G  /i-data/d895772b/Magne
96.4G   /i-data/d895772b/video
2.0T    /i-data/d895772b
2.0T    total
~ #

Best regards,

Magne