Reset to Factory Default

WD Sentinal DX4000 with 8TB, How much time required on drives formating?

at least 5 days, turn off windows update on your source pc so it does not reboot halfway done.

I have WD Sentinel DX4000 with 8TB (4x2TB), If I unpluged two hard drives from storage, then wahat happend. Is storage automaticaly rebuild RAID 1 or RAID will configure Manualy? If RAID will configured manulay how much take time? Please also send me any manual regarding RAID configuration.

If you have 4 drives and unplug 2 the box will die dead

is RAID 1 not configureable in this sitaution?

Yes you may configure the box by doing a factory reset.  This will take 5 days or so if you are lucky.  Then you may start adding users and data to the box.