How to Format a New Internal SSD in macOS High Sierra

Recently, some OWC customers have reported experiencing a situation where their new SSD will not show up in Disk Utility in High Sierra. Although Disk Utility should always be tried first, a Mac’s Terminal can be used to format the drive in these cases.

If the original drive was not upgraded to High Sierra, that should be done first so the internet recovery feature on the computer is updated to High Sierra.

Again, these instructions are intended for new internal SSDs only, with computers that have already had their original drive upgraded to macOS 10.13 High Sierra.

1) After the new SSD has been installed into the computer, boot to internet recovery by pressing Command-Option-R until a globe is seen. If the computer is not connected to the internet via an ethernet connection it will prompt for a wifi network to be chosen. It may take up to 10-15 minutes to complete the boot sequence, depending on internet speed.

2) Once at the macOS Utilities menu, select Disk Utility.

3) In the menu bar at the top of the screen click on the View menu and select Show All Devices. This should allow the SSD to show up in the left column, if it does not show up quit Disk Utility and reopen it.

• A) If the SSD does show up you may want to select the drive and click on the Erase tab. You can then name the drive and chose the desired format (APFS is the best choice) and partition scheme (GUID is the best choice). Once the format is complete the SSD is ready for the OS to be installed.
• B) If the SSD is not showing up Terminal sould be used to format the drive, which is outlined in the remaining steps.

4) Quit Disk Utility, then from the menu bar open the Utilities menu and select Terminal. Please read the notes below before proceeding:

Note: We strongly recommend that you disconnect any externally mounted drives at this point, to prevent accidentally destroying the data on those drives. For drives that cannot be disconnected, please make sure you have current backups of those drives.

When using terminal it is important to type all commands exactly as they appear in this guide. Making a typo could result in lost data and time.

5) In Terminal type the following command, then press the Return key:

diskutil list

6) A long list of disks will appear; we need to find our target disk from this list. An internal drive should be the very first or second drive in the list (see image below). The majority of the list is going to be ignorable disk images. To find the internal SSD, look for the following: ‘(internal, physical)’ which is shown in the blue box below. You can further confirm you have the proper drive by looking at the size (red box). You will need to note the identifier of that drive (green box) for the next step.

7) In Terminal type the following command using the identifier found in the previous step and hit the Return key.

diskutil eraseDisk JHFS+ MacOS /dev/identifier

The process normally takes a minute or two to complete. When the process is complete, you will see the following message: “Finished erase on identifier” where identifier was the number you previously identified.

The SSD has now been formatted as a Mac OS Extended (journaled) volume named ‘MacOS’. Continue using this guide to format the disk as an AFPS volume, however if a Mac OS Extended (journaled) volume is desired you may now stop.

8) From the previous step we need to note the identifier of the new volume (red outlined box). It’ll be mentioned in the “Formatting identifier as Mac OS Extended (Journaled) with name MacOS.”

In Terminal type the following command and hit the Return key: 

diskutil apfs createContainer /dev/identifier

The process normally takes a minute or two to complete. You’ll see the following message when done: “Finished APFS operation on identifier MacOS”

9) From the previous step, note the identifier from the newly created APFS Container (shown in the red box below) and use it in place of ‘identifier’ in the final Terminal command, shown below the screenshot.

In Terminal type the following command and hit the Return key:

diskutil apfs addVolume identifier APFS MacOS

The process normally takes a minute or two to complete. When the process is complete, you’ll see the following message: “Finished APFS operation on identifier.”

The SSD is now formatted as APFS and is ready to use.

Find more tips for macOS 10.13 High Sierra and 10.14 Mojave at the Rocket Yard!

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