Running MacOS 10.7.5 on a 27iMac. I just bought a new 4 TB WD Red SATA III 5400 HDD. When mounted on an external connection, the drive is seen (identified by model in the list: "WDC WD40EFRX-68W0N0 Media") by Disk Utility, but all the ERASE tab functions are 'grayed' out and cannot be operated. Anyone know what's up with this? Thanks!