cant install High Sierra onto external SSD - This disk doesnt use GUID partition scheme.

[madeirabhoy]

running high sierra from internal HD on 2011 iMac 27". bought a thunderbolt SSD to quicken my machine up as well as protect myself from the old HD failing sometime.

got it today. go to run MacOS High Sierra and the SSD along with one of the usb drives is greyed out. when i click on it i get

this disc doesnt use the GUID partition table scheme. use disk utility to change the partition scheme. select the device containing the disk, click on the erase button, select the volume scheme and click erase.

which i do. it offers me to change the format, but not the partition table. i select mac os extended journaled.

press erase. it works.

back to installation, still greyed out.

 

[Darmok N Jalad]

When using Disk Utility in High Sierra, look at the upper left corner for the “view” button and make sure it is set to view devices. From there, click on the device and erase. It will give you the option to select GUID. Sounds like what you are formatting is the volume, so there isn’t an option to change to GUID.