Question: Cannot erase Toshiba Canvio 3 ( 5 TB)
Trying to install new Toshiba hard drive. Selected hard drive in Disk Utility, picked Erase with Mac OS Extended format. Return immediately and the drive will not mount. Toshiba Tech Support had me restart iMac; on restart message said drive is not compatible, requested Initialize. This time tried MS-DOS (Fat) with same result. Drive will not mount. Under partition + and - are grayed.
iMac with Retina 5K display, macOS High Sierra (10.13.3), 16 Ghz Core i7