How to Migrate Your Mac’s OS and Your Data to a New Drive

Found this at OWC (, a DIY Guide to switching out Mac hard drives without losing your data — the very thing I’ll be doing one of these weekends to fit Battlefront II on my bootcamp partition (as Battlefront I is currently taking all the space).


Upgrading the original drive in your Mac is a great way to improve performance and/or increase the storage capacity of your machine. When transferring your data from one drive to another, we highly recommend you install a fresh copy of the OS, and then use Apple’s Migration Assistant to migrate your data to the new drive.

While drive cloning is also an option, performing a fresh OS install and migrating your data can provide a much better starting point to ensure that everything will work correctly, and should you have any issues with your new drive, it can eliminate additional variables to troubleshoot.

Performing a fresh install will also ensure your new drive is setup with the Recovery Partition that Apple creates during the OS install process.

Drive Migration
Special Note…

If you can’t attach your original drive externally, you can instead use a Time Machine backup when transferring files using Migration Assistant.

To Use a Time Machine Backup
Perform Steps 4-13 below, but use the Time Machine drive instead of your original drive for Step 5.


Choose the correct drive to install in your computer

Nothing will put the brakes on an installation like trying to install the wrong drive. Please double-check your Mac’s model ID before proceeding (press the Option key then choose Apple Menu > System Information). Once you know the model ID, use MyOWC to find the right drive. If you’re still not 100% sure, our sales representatives are happy to help.


Make sure you have a way to transfer your data

To transfer your data, you’ll need to have both your original drive and your new drive connected at the same time. For single-drive computers (e.g. most laptops), you’ll need a device to connect the old drive to your computer after your new hard drive is installed.

If you plan to use your old drive for external storage when the migration process is complete, you can install that drive into an enclosure. We offer many DIY kits with the external enclosure included. Depending on the size and connector type on your drive, you can use one of the following solutions to connect the drive: an External Enclosure, the OWC Drive Dock, or the Newer Technology Universal Drive Adapter. In some instances, though (most notably with MacBook Airs and Retina MacBook Pros), you’ll need a special enclosure for Apple’s SSD.

For those extremely rare cases where you can’t connect your old drive externally, the following steps will be slightly different. See the Special Note at the end of the article for more details.

If the Mac can hold both the new drive and the original drive (for example, a 2006-2012 Mac Pro, or a laptop or Mac mini with a Data Doubler) no enclosure should be necessary. Please contact our customer service team if you are still unsure of which solution is best.


Make sure you have a current backup

Make sure you have a current backup of your data on a separate drive before you continue. If you have a Time Machine backup already, you should be good to go. If you don’t use Time Machine, you can make a complete copy of your drive using these instructions in our Tech Center. This will ensure you have a separate copy of your data (i.e. a copy on a separate physical device), in the unlikely event of accidental data loss during the upgrade.


Make sure you have a means of installing an operating system (OS)

For Mac operating systems 10.6 or earlier, you will need the installer disc for the OS.

For 10.7 and later, you can use the recovery partition on the original drive. To make sure you have a functional recovery partition, restart your computer and immediately hold down the ‘Command’; and ‘R’ keys until the Apple logo appears. If your computer boots into a four-option menu then you have a functional recovery partition that can install the OS. If your computer boots normally to your desktop then you do not have a recovery partition.

For 10.7 users that do not have a functional recovery partition and have a computer found on this list (or which is newer than the computers on said list), then you can use the Internet Recovery feature built into your Mac. To make sure you have access to Internet Recovery, restart your computer and immediately hold down the ‘Command’, ‘Option’, and ‘R’ keys until you see a spinning globe or Apple logo. If your computer does not have an internet connection it will prompt you to connect to a wifi network. If your computer boots into a four-option menu then you have the ability to use Internet Recovery.

If all else fails then you can create a USB installer using DiskMaker X.


Install your new drive

If you need help installing your drive, OWC has an extensive library of instructional videos that walk you step-by-step through drive installation for most user-upgradable Mac models.


Connect your old drive externally
Note: Only for systems where the original drive has been removed. Systems that have both new and old drives inside the Mac can skip to Step 7.

Once you have replaced the old drive with the new one in your computer, connect the old drive to the external enclosure or adapter that you will be using, as mentioned in Step 2. Connect the now-external drive to your computer using the appropriate cable and proceed to the next step.


Boot to your installer

Boot to whichever installer method worked for you in Step 4.

Note: Aura Pro X drives require the ‘Command’-‘Option’-‘R’ or flash drive methods.

STEP #8a

Format your new drive (for OS X up to macOS 10.12.x)

Use Disk Utility to format the new drive. You can find Disk Utility in the Utilities menu at the top; in 10.7 and later, it’s also in the main list in the center of the screen.

Once Disk Utility is open, select the new disk from the list on the left. Once you have the disk selected, click on the ‘Erase’ tab on the right.

Set the Volume Format to ‘Mac OS Extended (Journaled)’; The name can be anything you want. Once those options are set, click the ‘Erase…’ button.

STEP #8b

Format your new drive (for OS 10.13 and newer)

Use Disk Utility to format the new drive. This will be Option 4 in the menu option that is presented when you boot up into recovery.

Once Disk Utility is open, select the View button on the upper left of the window and select Show all Devices. If your drive does not show in the sidebar, quit Disk Utility and then reselect it from the menu. Once you have the disk selected, click on the ‘Erase’ tab on the right.

Set the Volume Format to ‘Mac OS Extended (Journaled)’; for SSDs being installed as internal boot drives, select ‘APFS’ (Apple File System). NOTE: Rotational drives and Fusion drives can only be formatted as Mac OS Extended (Journaled). The name can be anything you want, but should be a different name from the startup drive being replaced. Once those options are set, click the ‘Erase…’ button.

STEP #9a

Restoring the OS and user data from Time Machine

For those using 10.7 and newer. Once the drive is formatted you can opt to select Restore from Time Machine. This method allows you to restore the OS and your user information back to the drive. Once this process is complete you can skip to Step 11.

STEP #9b

Installing a clean copy of OS X / macOS on your new drive

Once you’ve formatted the drive, you can close Disk Utility. If you’re in 10.7 or later, you’ll need to select the ‘Reinstall Mac OS X’ option from the Utilities screen. In earlier OS versions, quitting Disk Utility will take you back to the installer.

Follow the steps as they are presented, making sure to select the new drive (the one you just formatted in the previous step) as the install location. The OS installers are simple to use; all you need to do is follow the on-screen prompts. Once you have filled in the required information, the installation will begin. This can take quite a while, depending on your internet connection speed. Fortunately, the process at this point is automated, so you can do something else while waiting for the install to complete.

STEP #10

Use Migration Assistant to transfer your data to the newly installed OS on your drive

Once the OS has been installed, your computer will restart to the new drive and walk you through the final setup steps. Continue through the on-screen prompts until you’re asked if you’d like to import user data from another system. This part of the setup process uses Apple’s built-in Migration Assistant utility. If for some reason you skip the initial setup, you can find Migration Assistant by navigating to Applications > Utilities.

The Migration Assistant will scan for available drives, showing you a list. Select your drive once it appears, then click ‘Continue’.

The next screen will list the data types you can transfer. Select any users you want to bring over to your new drive, as well as any applications and network settings. You can either select them all, or you can select/deselect items individually by expanding the folders via the disclosure triangles. There is an option for ‘Files and Folders’ which you will likely want to copy over as well, since some applications install some settings in non-standard places.

Once you have selected the items you would like to copy to your new system drive, click the ‘Transfer’ button. Depending on how much data is being is being copied, this may take a while. After Migration Assistant finishes you can continue the rest of the process. Once the setup is complete your computer will bring you to the login screen or your desktop.

STEP #11

Run Software Update on your new installation

In most cases, there will be updates immediately available for the OS version you just installed. Once the initial setup has completed, follow the normal process for updating, based on your OS version (some version will require you to open the App Store application, others can be updated by choosing Apple > Software Update…. Restart if necessary and repeat the process until there are no more updates to install.

STEP #12

Repair disk permissions

Note: if you are using macOS 10.12 or newer skip to Step 13.

For OS 10.6-10.11: Use Disk Utility (Applications>Utilities>Disk Utility) to repair permissions on your new drive. Select the new OS X volume in the list on the left, then click on the ‘First Aid’ tab, then click on ‘Repair Disk Permissions’.

STEP #13

Double-check your files

Run all your apps and go through your files to make sure everything is working and nothing is missing. You may have to re-authorize some applications or, in very rare cases, reinstall the application. Make sure everything is as you want it before continuing.

STEP #14

You’re Done!

Once you’ve checked to make sure your data came through correctly, you’re ready to go. Now you can either erase your old drive in the external enclosure and use it for other purposes or save it for posterity.

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