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How to Use SSD as Boot Drive and Hard Drive as Storage on Mac?

I have a 1TB 5400 RPM HDD. Does anyone know how to use SSD as a boot drive and have HDD in an optical bay as storage on a Mac? I mean both drives work as one. Please let me know if you have a solution.

Best Answered by

Alin· Answered on Jan 21, 2026

You can use SSD as a boot drive and have HDD as storage on a Mac. But it's not recommended to use them as one because they are basically two separate drives. Of course, you can change the location of a User folder to another drive. But it's dangerous and requires the command line to accomplish the task.

If you want to use SSD as a boot drive and have HDD as storage separately, you can follow the steps below:

Use SSD as Boot Drive:

1. Back up your Mac with Time Machine and iCloud. You can also do it using EaseUS Todo Backup.

2. Connect your external SSD to your Mac. Go to Applications > Utilities > Disk Utility, and select View > Show All Devices.

3. Select the external SSD entry at the top of the list and click Erase.

4. Click Erase after making sure the name, format, and scheme are as follows:

Name: Macintosh HD
Format: APFS
Scheme: GUID Partition Map

5. Now you can install macOS on your external SSD.

Use HDD as Storage:

Plug the hard drive into the Mac using the cable that came with it. And double-click it to open the drive to view its contents.
Select the hard drive from the left menu. Click the Erase button at the top of the Disk Utility window.
Select ExFAT from the Format menu. Click Erase to format the drive with the selected format.
Once the drive has been formatted properly, it will appear on your desktop. You can add files to it now.

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