The clean method of installing OS X Yosemite wipes all the data from the destination drive and replaces it with the fresh, never-before-used data from the OS X Yosemite installer. All your user data and any applications that you installed will be gone. While the clean install option may not sound like a friendly way to update a Mac to OS X Yosemite, it offers advantages that make it the preferred update path for some Mac users.
The Benefits of Performing a Clean Install of OS X Yosemite
If your Mac suffers from annoying problems that you’ve been unable to fix, such as occasional freezes, unexpected shutdowns, applications that hang or seem exceptionally slow, or poor overall performance not attributed to hardware issues, a clean install may be a good choice. Many of these problems can occur over the years of using your Mac. As you upgrade systems and applications, debris is left behind and files become large. This causes slowdowns and may corrupt some system files. Finding these bits of file debris is almost impossible. If you encounter these kinds of problems with your Mac, a good clean sweep may be the remedy your Mac needs. Sometimes, the cure may be worse than the problems. Performing a clean install deletes all the data on the destination drive. If the destination is your startup drive, which for most users it will be, there goes personal data, settings, preferences, and apps. However, if a clean install cures the problems, the tradeoff may be worth it.
Back Up Your Data
No matter which installation method you choose, back up your data before proceeding. A recent Time Machine backup is the bare minimum you should have on hand. Also, consider creating a clone of your startup drive. That way, if anything terrible happens, you can recover by booting from the clone and be back where you started, without taking the time to restore the data from a backup. A clone is also an advantage when it’s time to migrate your information to your new installation of OS X Yosemite. The Yosemite Migration Assistant works with cloned drives and lets you easily move data you may need.
What You Need for a Clean Install of OS X Yosemite
Here’s what you’ll need to perform a clean install:
The Yosemite installer on a disc or as a downloaded image file. If you can’t find Yosemite in the store, check the Purchase page. If you ever downloaded Yosemite in the past, it will be listed there. A Mac that meets the minimum requirements for OS X Yosemite. A recent backup of your current Mac startup drive. A startup drive that contains OS X Snow Leopard (10.6) or later and which you’re willing to erase.
Clean Install of OS X Yosemite: Boot From USB Flash Drive to Start the Process
With the preliminary steps out of the way, you’re ready to start the process.
Create a Bootable Version of the Yosemite Installer
Now that you have the OS X Yosemite installer downloaded to your Mac, the next step is to make a bootable copy of the installer on a USB flash drive. You need a bootable version of the installer because you’ll erase your startup drive as part of the clean install process. To erase and reformat the startup drive, start your Mac from another device. Since all OS X installers include Disk Utility and an assortment of other apps, booting from the Yosemite installer allows you to erase the startup drive and perform the installation, all from the same USB flash drive. Once you finish creating a bootable version of the OS X Yosemite installer, come back here to continue the clean install of OS X Yosemite.
Boot From the USB Flash Drive
Follow these steps to boot the installer from a USB flash drive. You’re now ready to start the OS X Yosemite installation process.
Clean Install of OS X Yosemite: Complete the Installation Process
In the previous steps, you erased the Mac’s startup drive and returned to the OS X Utilities window. You’re now ready to complete the installation process by letting the installer copy the OS X Yosemite system files to your selected startup drive. Once everything is copied, your Mac reboots into Yosemite and walks you through setting up your admin account, migrating data from a previous version of OS X, and other general housekeeping tasks. Your Mac finishes the setup process and then displays your new OS X Yosemite desktop. Have fun, and take time to explore all the new features.
