If your disk doesn't appear in Disk Utility, disconnect all nonessential devices from your Mac. If the disk is external, leave it connected, but make sure that it's turned on and connected directly to your Mac using a good cable. Then restart your Mac and try again. You can erase a disk or a volume on that disk at any time, including in circumstances such as these:.
Are you formatting the disk that came built into your Mac? Are you about to install macOS High Sierra or later on the disk?
If you need to erase your disk before installing High Sierra or later for the first time on that disk, choose Mac OS Extended Journaled. During installation, the macOS installer decides whether to automatically convert to APFS—without erasing your files:. Are you preparing a Time Machine backup disk or bootable installer?
How to Reformat Your MacBook Pro
Will you be using the disk with another Mac? Disk Utility tries to detect the type of storage and show the appropriate format in the Format menu.
Open Menu Close Menu Apple. How to erase a disk for Mac Use Disk Utility to erase format a hard disk, flash drive, or other storage device for Mac.
How to erase a disk Disk Utility can erase disks, add volumes, check disks for errors, and more. You can also find it in the Utilities folder of your Applications folder.
I have a very weird problem - I messed up with the partions when I installed Bootcamp. Now, how can I reformat and install OS X from the installer placed in the external hard drive?
MacBook acting up? Reformat it and get it back on track
Muhammad Umar Muhammad Umar 1 1 gold badge 2 2 silver badges 3 3 bronze badges. From there, you can reinstall Lion. Alternatively, you can use the standard Recovery HD. Both are outlined and documented here: macworld. You can erase the drive and reinstall OS X using the recovery system : Start up from the recovery partition by holding command-R. It also erases the hidden recovery and EFI partitions.
Format an External Hard Drive or USB Flash Drive for Mac OS X
Reinstall OS X. But if you restart the Mac, it will start up in Internet Recovery mode, which means that it downloads a disk image of the recovery system from Apple's servers, and you can then install OS X on the empty drive. If others search for how to do a normal erase and reinstall, erase the main OS X partition like Macintosh HD instead of the whole drive: Start up from the recovery partition by holding command-R.
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How to Reformat a MacBook