Connect your drive to the Mac. Quit all other applications on the Mac, especially those that may be trying to access the external drive (e.g. IPhoto, Words) Launch Disk Drill. Click on the external drive that you are trying to recover files from. If it has partitions, you will see all of them. Some Mac users may wish to create a bootable MacOS Catalina installer drive, typically using a USB flash drive or with another similar small boot disk. Bootable USB installers offer an easy way to upgrade multiple Macs to macOS Catalina, to perform clean installs of MacOS Catalina, to perform maintenance from a boot disk like formatting disks.

1. Google Drive Mac
2. D.u.i. Drive Mac Os Flash Drive

Reader Ben Connolly is interested in keeping some distance between his Mac’s operating system and data. He writes:

Google Drive Mac

I’m planning to get a new Mac and I’d like to keep my system on one drive (perhaps an SSD) and my data on another drive. How do I go about this? Is it possible to keep my Home directory on a drive other than the startup drive?

D.u.i. Drive Mac Os Flash Drive

It is. In the past you’d copy your Home folder to the other drive and then point to it via symbolic links but that’s no longer necessary. When setting up your new Mac I’d do this.

Run through the usual setup process. Once you’ve completed that process connect the drive you’d like to save your data to. Copy your user folder from the Users folder at the root level of your hard drive to the external hard drive. (You’ll have to enter your username and password to authorize this.) Launch System Preferences and choose the Users & Groups preference (called Accounts in versions of Mac OS X prior to Lion). Click the Lock icon at the bottom of the window and enter your administrator’s name and password and click Unlock.

Hold down the Control key, click on your account name, and choose Advanced Options. In the sheet that appears, click on the Choose button next to the Home Directory field. Navigate to the home folder you moved to the external drive, select it, and click Open. You’ll see that the path to that folder now appears in the Home Directory field—/Volumes/DriveB/yourusername, for instance. This is your new home folder. Anything that’s normally saved in your home folder—pictures, movies, documents, music, and preference files—will be stored here.

Test the account to ensure that it’s working properly. For example, launch iTunes and make sure that an iTunes folder is created in the Music folder within this home folder. Once you’re satisfied that everything’s working correctly, you can delete the original home folder on your startup drive.

We’re not quite finished. Return to the Users & Groups system preference and create a new administrator’s account. Why? If your external hard drive goes kablooey and your internal hard drive lacks a user folder, you won’t be able to boot that drive into a fully functioning account. With that extra account, you can.

These key combinations apply only to Mac computers with an Intel processor, not Mac computers with Apple silicon.

To use any of these key combinations, press and hold the keys immediately after pressing the power button to turn on your Mac, or after your Mac begins to restart. Keep holding until the described behavior occurs.

• Command (⌘)-R: Start up from the built-in macOS Recovery system. Or use Option-Command-R or Shift-Option-Command-R to start up from macOS Recovery over the Internet. macOS Recovery installs different versions of macOS, depending on the key combination you use while starting up. If your Mac is using a firmware password, you're prompted to enter the password.
  
• Option (⌥) or Alt: Start up to Startup Manager, which allows you to choose other available startup disks or volumes. If your Mac is using a firmware password, you're prompted to enter the password.
  
• Option-Command-P-R:Reset NVRAM or PRAM. If your Mac is using a firmware password, it ignores this key combination or starts up from macOS Recovery.
• Shift (⇧): Start up in safe mode. Disabled when using a firmware password.
• D: Start up to the Apple Diagnostics utility. Or use Option-Dto start up to this utility over the Internet. Disabled when using a firmware password.
• N: Start up from a NetBoot server, if your Mac supports network startup volumes. To use the default boot image on the server, hold down Option-N instead. Disabled when using a firmware password.
• Command-S: Start up in single-user mode. Disabled in macOS Mojave or later, or when using a firmware password.
• T: Start up in target disk mode. Disabled when using a firmware password.
• Command-V: Start up in verbose mode. Disabled when using a firmware password.
• Eject (⏏) or F12 or mouse button or trackpad button: Eject removable media, such as an optical disc. Disabled when using a firmware password.

If a key combination doesn't work

If a key combination doesn't work at startup, one of these solutions might help:

• Press and hold all keys in the combination together, not one at a time.
• Shut down your Mac. Then press the power button to turn on your Mac. Then press and hold the keys as your Mac starts up.
• Wait a few seconds before pressing the keys, to give your Mac more time to recognize the keyboard as it starts up. Some keyboards have a light that flashes briefly at startup, indicating that the keyboard is recognized and ready for use.
• If you're using a wireless keyboard, plug it into your Mac, if possible. Or use your built-in keyboard or a wired keyboard. If you're using a keyboard made for a PC, such as a keyboard with a Windows logo, try a keyboard made for Mac.
• If you're using Boot Camp to start up from Microsoft Windows, set Startup Disk preferences to start up from macOS instead. Then shut down or restart and try again.

Remember that some key combinations are disabled when your Mac is using a firmware password.

Learn more

• Keyboard shortcuts that you can use after your Mac has started up.