Why does the full reset take more than 19 hrs

I have a problem, I am trying to reset my WD Cloud but it takes now already more than 19 hrs. Is that what it takes?

The ‘full factory restore’?

It does multiple overwrites to all available disk space. This will take some considerable time.

Assuming you have a 4TB drive, and it is able to write at 100MB/s, one write pass will take 4e12/100e6 = 40k seconds = 11 hours.

100MB/s is a guess, based on the reported maximum write speed people generally encounter over the gigabit ethernet port.

Thanks for the explanation but it is now actually overall 30 hrs. Guess that is a bit long but I just let it keep going.