@Svilen I have a similar issue with the same hard drive and router (though older version v2)... except mine recognizes it, just shows space of only 196MB for a 4TB hard drive! I know this doesn't...

I purchased a new 4TB hardrive and formatted it NTFS. It's a Seagate Backup Plus Portable. I plugged it into the second USB port (I already had a smaller hard drive) and it's showing as only 196GB...