How to partition your Mac to test OS X Yosemite

How to partition your Mac to test OS X Yosemite

Installing Yosemite? It's a beta. Put it somewhere it's not likely to cause problems — here's how

Regardless of whether you're using the Developer Preview or the forthcoming public beta, bear in mind that OS X Yosemite is beta software. It's best not to install it as the primary operating system on your only Mac, so here are instructions for making a new partition to run it from.

This way, Yosemite will be isolated from the rest of your Mac — even if something drastically bad happens, the only bad thing that should happen will be to that partition, not to your entire machine.

Before you partition your drive or install Yosemite on your Mac, back it up using Time Machine or another method.

Partitioning your hard drive will reduce the amount of available space for Mavericks, so make sure to give yourself some wiggle room. What's more, make sure to give yourself enough space to run Yosemite effectively.

How to partition your drive

  1. Open the Utilities folder.
  2. Double-click on Disk Utility.
  3. Select your hard drive volume in the upper left hand corner of the sidebar.
  4. Click on the Partition button.
  5. Click the + button.
  6. Size the partitions based on free space, and bear in mind what I said about wiggle room.
  7. Click on the Apply button.
  8. Disk Utility will then check the disk and make changes. This will take several minutes.
  9. Quit Disk Utility.

Once your drive is partitioned, you can install Yosemite on the new partition. The Yosemite installer will give you the opportunity to import settings from your Mavericks partition — as tempting as it is, don't do it. To effectively test Yosemite, make sure to keep it a clean install. That way you know you're not introducing problems from previous installations.

Once you're done with Yosemite and you want to get things back to the way they were, you can delete the partition and resize your Mavericks partition back to the whole disk. To do so, follow these instructions.

First of all, make sure you've booted using your Mavericks partition. Turn on (or restart) your Mac holding down the Option key and select the drive icon that corresponds to Mavericks.

How to remove and resize partitions

  1. Open the Utilities folder.
  2. Double-click on Disk Utility.
  3. Select your hard drive volume in the upper left hand corner of the sidebar.
  4. Click on the Partition button.
  5. Select the Yosemite partition.
  6. Click the - button.
  7. Disk Utility will ask you to confirm removal of the partition. Click the Remove button.
  8. Resize the Mavericks partition by clicking its lower right hand corner and dragging down until it fills the entire partition space, then click Apply.
  9. Once it's done, quit Disk Utility.

Disk Utility makes it pretty easy to create and delete disk partitions without risking data on your Mac's primary boot volume, but there's always a chance you can run into a problem — everything from a device error to a software issue, unexpected power outage and more. That's why I have to emphasize that you should always back up your Mac before attempting any operation like this. Having said that, if you follow these instructions, you should be okay.

Have you installed OS X Yosemite? Did you do it in a new partition or on a separate disk all together? Let me know if you have any questions.

Have something to say about this story? Leave a comment! Need help with something else? Ask in our forums!

Peter Cohen

Mac Managing Editor of iMore and weekend Apple Product Professional at a local independent Apple reseller. Follow him on Twitter @flargh

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Reader comments

How to partition your Mac to test OS X Yosemite


Good and accurate info, but frankly it seems insane to me to install a beta OS on anything other than a totally separate physical drive.

Sometimes it can be hard to get the original boot volume back to how it used to be.

I have a dual-drive iMac with 250 GB SSD and 2TB disc. Any advantage to partitioning one or the other?

What about using a large capacity USB stick as an alternative?

Any advantage to partitioning one or the other?

Speed, mainly. You may be rebooting more frequently with the beta, and an SSD can shave some time off that.

What about using a large capacity USB stick as an alternative?

It's kind of a PITA. I'll see if I can distill it down for a separate how to.

Do not do this if you are running a boot camp windows partition. It will **** that **** up!

Sent from the iMore App

If your partition turned into Logical Volume Group (you can't resize or delete Yosemite partition), you can revert partition type with few command line.

Open Terminal
type "diskutil corestorage list"
Find Yosemite partition UUID string.

type "diskutil corestorage revert <UUID>"

Your Yosemite partition is now revert to default partition type. Now, you can resize or delete yosemite partition :)

It says the volume is not revertible. It gives me this error code. Any suggestions?

Error: -69741: The target disk isn't eligible for reversion because it wasn't created by conversion or it is not part of a simple setup of exactly one logical and one physical volume

Thanks so much for the advise. I entered those comment lines, and it sort of worked. I now see my Yosemite partition the way it should, but it is red and it says "not activated". I also can't activate it. And I still see yosemite as a Logical Volume Group. Do you know what I could do to fix it?

This is the approach I took. Sometimes I use old hardware. But sometimes you need newer hardware (for bluetooth LE and continuity, for example), and that's when I use the partition approach.

Hey Peter,

When I partitioned my drive it renamed the Logical Volume Group to the same name of my new partition. I researched it but do you know of a way to rename the group without reformatting the entire disk?

My harddrive reads as:

>OS X Yosemite
-Machintosh HD
-OS X Yosemite

Read my comment above :)

in terminal type "diskutil corestorage list" and find your Yosemite partition UUID
then type "diskutil corestorage revert <UUID>"

now, your whole disk revert to default partition format. No reformatting. your data and files are safe

I installed Yosemite on a partition of a external hard drive. It seems safe enough for me to attempt to use it for daily use and I'd like to keep the external copy to test with.

I tried to download it again to install on my iMac main drive. The App Store says my redemption code has already been used and won't let me download it again. What is the best way to reinstall it to my main iMac drive?