Sometimes you need an emergency startup disk, or an alternate startup disk for testing your Mac. Read on for more information on how to create a diagnostic startup disk with Intel Macs. For Apple Silicon Macs, see this knowledge base article.
eDrive – Start up from a diagnostic partition
The eDrive tool allows you to add a separate startup partition on your startup disk that you can use for emergency startup and testing and repairing your internal drive. Simply choose where you would like to create the eDrive from the eDrive Destination Volume, and then click Create eDrive. A partition will be added to the selected disk, and then a data from your hard drive will be copied to your eDrive to serve as the system for the new partition.
Techtool Pro – eDrive

Protogo – Start up from a flash drive
The Protogo tool allows you to add a separate startup drive – usually a thumb drive – that you can use for emergency startup and testing and repairing your internal drive. Select the device you want to use (all data will be erased), the profile you want to use (the Basic Profile is the most common), and then click Build Techtool Protogo Device.
Techtool Pro – Protogo

Next Steps
Once you have created your eDrive or Protogo device, hold the option key at startup to choose it as your startup disk. When finished with testing or repair, restart your Mac normally.
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