With the recent release of OS X Yosemite Beta, Mac users that signed up for the Beta Seed Program are running to get their own copy. While this is great, most of us don’t have a second Mac that is new enough to run OS X Yosemite, and with being a beta version, it’s not recommended to be installed on your main Mac.
While you can install the beta to a second partition, there have been some complaints about the Yosemite beta not playing nice with partitions. To keep your Mac safe while still getting to see the new OS, your best bet is to install the OS X Yosemite beta on an external drive. If you’re interested in trying it out, here’s how.
Note: It’s worth noting here that when you run an OS from an external drive performance will definitely see a decrease. Don’t run this beta from an external drive and expect perfect speed and performance. Depending on the speed of your drive you may see a very slow system.
Download the Beta
If you haven’t downloaded the OS X Yosemite beta yet, head over to Apple’s site for it and download it. Scroll to the bottom of the page and click Get OS X Yosemite Beta Redemption Code. You do have to be signed up for the Beta Seed Program, so head to this link to do that first, if you haven’t already.
When you click the Get OS X… button you’ll be taken over to the Mac App Store where the code will be verified and your download will begin. Once the beta has finished downloading (all 5GB of it) you’re ready to move to the installation phase.
Preparing the Drive
While the beta is downloading, take some time to prep your external drive. First, you need to make the drive bootable. To do this, plug the drive in and open up Disk Utility from your Applications/Utilities folder.
Click on the external drive in the list to the left and click on the Partition tab, click the Partition Layout dropdown box and choose 1 Partition. Next, click the Options button and make sure GUID Partition Table is selected. Click OK, Name your drive something memorable like Yosemite Beta, then click Apply.
With your new partition set and your drive erased, it’s time to install the Yosemite beta.
Install OS X Yosemite Beta onto the External Drive
Once the Yosemite Beta has finished downloading, the installer should automatically launch. Click Continue to begin.
Next you’ll be presented with a long license agreement that we’re sure you’ll read 100% of the way through, so once you’re done with that, click Agree to continue.
Here’s where things start to get important. You should now see the disk selection screen. Click Show All Disks and select the drive you just re-partitioned and named, then click Install. You’ll be prompted for your OS X password and once you enter it, the install will begin.
Once installation is complete, you’ll walk through a similar installation process as you did with Mavericks. Follow the steps to gain access to Yosemite. The final setup steps are not difficult to walk through and should take only a few minutes.
Note that you must change the startup disk before exiting Yosemite, or by holding down Command+R during restart to get into Recovery Mode. Here, click on the Apple menu and choose Startup Disk. Choose your Mac’s hard drive and restart again. If you don’t do this you’ll t stuck in an install loop. Make sure to reset your startup disk as your Mac hard drive.
Hold down the Option button on your keyboard to see a list of startup disks to pick from when you want to boot into your Yosemite beta installation.