Format Backup Drive For Time Machine Disk Utility Mac Guid Partition Map
Select the GUID Partition Map if you are creating a bootable install Disk or going to use with Time Machine backup. And then click on “Erase” to erase and format the external disk or Flash drive. Formatting an External Disk or a Flash Drive for Mac. Go into Disk Utility, (Applications > Utilities > Disk Utility) and select the External Seagate Drive. Make sure the partition map is set to GUID Partition Table, and the Volume is Mac OS Extended (Journaled).