A couple of days ago I decided it was time to try a modern Linux distro. As a newcomer to Linux, I decided to preserve the pre-installed Windows, just in case. Luckily, my laptop has two SSDs, which I planned to use to completely isolate the files of the two operating systems.
So I chose Fedora, managed to clear some free space in one SSD, created a live USB and booted from it. Everything went smoothly until the Anaconda installer told me to select an installation method.
Okay, I know where the new system is going, and I know something about the EFI partition, so there should be little problem…but wait - what does the destination mean? If I choose only the desired SSD, will the exisiting EFI partition be updated correctly? (It seemed not.) Also, there is still a non-empty partition on that SSD, will the installer just ignore it and wipe out everything? (That also seemed not.)
I did find the integrated disk manager, but the “USE IT AT YOUR OWN RISK” warning immediately scared me away.
My final solution is to iterate through all possible combinations, and guess if everything is ok by the summary given before actual installation. 
Thankfully the summary is at least consistant with my intuition, and everything is working fine now.
There are already bunches of complaints about the new installer, but I think my specific experience (and my confusions) might still be worth sharing, since I wasn’t doing a simple “fresh install”.
Here are the working settings for me, in case anyone is interested.
- Destination: all the two disks, to let the installer locate free space and EFI partition.
- How would you like to install: “Share disk with other operating system”.
- Reclaim space: leave this empty as the free space was already researved and had not been formatted.