Yardie (and D-Link technical support), a strange thing happened.
The formating was stucked at 94% when I went to bed last night (after many hours); this morning, I see 74%.
It seems that the formating restarted without any intervention

Overall, the format has been going on for almost 24H so far.
When I log into the device (Web interface), I'm welcomed with the "HARD DRIVE CONFIGURATION" page.
Anybody experienced this?