To play it safe, I would recommend making your second partition at least 20 GB large (I chose 50 GB).Īlso, you may want to make a bootable install USB drive of Yosemite just in case you need to try again, or want to install it on another one of your computers without downloading the install file again from the Mac App Store.
It's also stated that Yosemite only needs 8 GB of available storage, but in my case, after installing Yosemite on my second partition, it reads just over 13 GB used.