Hello, community engineers.
This issue is resolved and leaves a solution.
- I connected the problematic abnormal hdd and even completed booting.
Afterwards, qnap started automatic recovery, removing the abnormal hdd, and replacing the abnormal hard with a known-good hard.
After that, we proceeded with the factory reset and confirmed that the hdd is connected normally.
If anyone is struggling with that problem, I recommend you to make one extra hdd.
Yes) Install 1,2,3,4 hdd → Replace 1 hdd → Store 1 hdd extra
I would like to sincerely thank the community for their help to the stranger in faraway Korea.
best regard