What Is Target Disk Mode? How and When to Use It on Your Mac
Best bet is to always backup your Mac hard drive with a bootable image created by Apple Disk Utility or a third party utility such as Carbon Copy Cloner. The easiest way to keep your files backed-up is by using Time Machine, which is built in to the Apple OS. The only requirement for Time Machine is to have an attached hard drive to back your files up to.
If you don't have a bootable backup, or a way to get a Mac drive, you will need to boot the computer from another operating system. First, try to boot your Mac in Recovery mode, holding down Cmd-r on restart. Secondly, you can try to boot your Mac into Safe mode to see if you can boot to a minimal desktop. Start or restart your Mac. Click the Restart button.
Boot from an External Drive On MacBook Pro
The usual course of action to salvage the internal drive is to install the drive in an external enclosure , take it to another Mac, and try any data recovery or repair utilities you may have. Target Disk Mode allows you to perform the same process, while skipping the disassembly of the Mac and the installation of the drive in an external enclosure. Migration Assistant: Another thing you can do with Target Disk Mode is use Migration Assistant to copy settings and user data from the drive to your new Mac.
Migration Assistant will consider the Target Disk Mode drive to be just another startup drive that has a valid system installed on it.
How to select a different startup disk
This can be helpful if your Mac has a problem with its own internal drive, and you need to be able to boot the Mac in order to reinstall the OS or perform repairs. The process for booting from a Target Disk Mac is mostly the same as described above; connect the two Macs together and boot one Mac in Target Disk Mode.
The difference is that instead of just starting up the second Mac, you hold down the Option key while starting up. Select the disk that corresponds to the target disk. Booting will then continue, using the operating system installed on the target Mac. The two Macs should be of the same year and model. Different models and years have different support for internal hardware.
The operating systems should be the same. This is similar to the first item. A firmware password: If the Mac has a firmware password set, it will not be able to enter Target Disk Mode. Name required. Email required. Save my name, email, and website in this browser for the next time I comment. Notify me of follow-up comments by email.
Notify me of new posts by email. Firstly, it allows you to run another copy of OS X without needing any additional Mac computer.
Firmware password protection
Also, since you can run a full copy of OS X on the external drive, it can be used for troubleshooting purposes on other Macs or it can be as a kind of virtual OS X. Using an external drive, you can save space on your Mac, though it might be a bit slower if you are using USB 2. To do this, open Disk Utility and connect the drive to your Mac.
Under External in the left hand menu, click on your external hard drive and then click on the Erase button. Make sure you backup any data before you erase the drive. When you click Erase, a dialog will pop up where you can configure some options.
How to Enter Target Disk Mode
It should only take a minute or two for the drive to be erased and reformatted. Now your drive is ready for OS X.
Go ahead and click the Download button to start downloading the installer. Just click Continue.
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