Hoping for some expert help!
I have new 12tb My Book Pro cannot be seen by Mac. “WD disk utilities” runs away and consumes all the Mac RAM memory over several minutes. The drive shows up under thunderbolt in System Information, or under USB in System Information, but WD Disk Utility cannot see it when connect by USB; when connected by thunderbolt it reports RAID error, and says to connect by USB to fix (which does not work, of course). Tried it on two computers, and both Sierra and El Capitan. I have older My Book Pro that works perfectly on same machines/systems.