Partition Fusion D. How to do it? Will this work?

[Racineur]

Hello, I have an Imac late 2012, 3.2 i5, 1T Fusion Drive. Mountain Lion 10.8.5 installed. Works flawlessly. But I would like now to give a try to Yosemite and maybe later to EC. But my Mac is so stable that I'm a bit anxious about upgrading directly to Yosemite via Apple Store. In another thread, I was suggested to partition the drive and install the new system. DU warns the disk in my iMac can be partitioned only in two. Ok, good for me. Questions: will the Mountain Lion hidden restore partition will be erased? Where will end up my apps and docs? Last, will the installer from the Apple Store let me chose the new partition for installing Yosemite? For now, I don't want to erase or lose the ability to boot with ML if I chose so. Newbie question I guess but I never partition a disk before. I am very "try before you buy".
Thanks in advance

 

[Fishrrman]

"will the Mountain Lion hidden restore partition will be erased?"

No. It will stay where it is.
Be aware that installing Yosemite will probably create a SECOND recovery partition of its own. You'll have to deal with two of them.

"Where will end up my apps and docs?"

There will be copies on BOTH partitions, with each OS, assuming you "migrate" your current stuff to the new Yosemite partition as well.

"Last, will the installer from the Apple Store let me chose the new partition for installing Yosemite?"

It should. Pay attention when the installer asks you to select the "target drive" to which to install.

More thoughts:
What you propose to do is better than just doing an "upgrade" to Yosemite over your existing OS.
If things don't work out, you can always just erase the experimental install and start over.

An even better approach might be:
Don't partition the internal drive.
Instead, install Yosemite onto an EXTERNAL DRIVE for the time being, and boot and run that way. It will boot and run slower than if it were installed onto the internal drive, but, doing it this way will provide you with "an extra level of insulation" from problems.

Personal experience:
I'm still using Yosemite "in experimental mode" with 10.8.5 currently as my "main OS".
Yosemite does "look different", but I've become quite pleased with how well it works. And I boot and run it from an external HDD in a firewire800 enclosure....

 

[Racineur]

Hello and thanks for the precious info. I really have to know if the Apple Store installer will let me chose the drive before installing Yosemite. I ordered an external SSD in order to try out Yosemite. Is there a way to know if the installer will let me do what I want before starting the process of upgrading?

 

[Bruno09]

I really have to know if the Apple Store installer will let me chose the drive before installing Yosemite.

Yes no problem, you will be able to chose the drive where you want to install Yosemite.