Most USB flash drives are formatted for use with Windows. Before you can install OS X on a USB flash drive, you will need to change the drive’s formatting to the standard used by OS X (Mac OS X Extended Journaled).
Format Your USB Flash Drive
- Insert the USB flash drive into your Mac’s USB port.
- Launch Disk Utility, located at /Applications/Utilities/.
- In the list of drives attached to your Mac, select the USB flash drive device. In my case, it’s called 14.9 GB SanDisk Cruzer Media. (Like lumber, hard drives and flash drives are actually slightly smaller than their specs would have you believe.)
- Click the ‘Partition’ tab.
- Select ‘1 Partition’ from the Volume Scheme dropdown menu.
- Enter a descriptive name for your flash drive; I chose Boot Tools.
- Select Mac OS X Extended (Journaled) from the Format dropdown menu.
- Click the ‘Options’ button.
- Select ‘GUID Partition Table’ from the list of available partition schemes.
- Click ‘OK.’
- Click the ‘Apply’ button.
- A sheet will drop down, warning you that you are about to erase all data from the disk. Click ‘Partition.’
- Disk Utility will format and partition your flash drive.
- Quit Disk Utility.
Warning: All data on your flash drive will be erased.
Enable Ownership of Your USB Flash Drive
In order for a drive to be bootable it must support ownership, which is the ability of files and folders to have specific ownership and permissions.
- Locate the USB flash drive on your Mac desktop, right-click its icon, and select ‘Get Info’ from the pop-up menu.
- In the Info window that opens, expand the ‘Sharing & Permissions’ section, if it’s not already expanded.
- Click the lock icon in the bottom right corner.
- Enter your administrator password when asked.
- Remove the check mark from ‘Ignore ownership on this volume.’
- Close the Info panel.