So I downloaded the Public Beta for High Sierra and was curios to see if an upgrade to APFS would function with my homemade Fusion Drive containing of an external Samsung drive enclosed in a LaCie Rugged Thunderbolt enclosure and the built-in harddrive @ 7200 rpm inside my iMac. Turns out that by checking the "convert to APFS"(my translation) button in the installer and doing an upgrade from a macOS Sierra installation that's been used quite a bit with csrutil disable and other things before being cleaned and only having csrutil disable on. Nothing else. I cleaned it up with the Maintenance app from TitaniumSoftware before running the macOS High Sierra. Just to say that I did my part in a trouble free install as possible. However, after the installation program rebooted my Mac I learned that my iMac wouldn't boot because I was given the "no boot" sign after waiting for an hour or so for the installation to finish. The installation progress would switch between an actual installation time and an estimated progress time. That ended up with a "no boot" sign. I tried many things within the installed High Sierra recovery partition that amazingly did get installed and nothing I could do with the 'diskutil apfs' command line did what is required to get back on track. My installation was totally smashed and I ended up taking apart the fusion drive (which was also smashed) re-installing macOS Sierra 10.12.5 from a USB-stick. I installed macOS Sierra on the SSD from Samsung, as mentioned before. No Fusion Drive this time. I then again checked the box to convert the filesystem to APFS - I really wanted APFS as you might have known by now Nothing succeeded this time around either. The Mac wouldn't finish the installation here either - waiting and waiting for an hour again this time. I then tried one last time with the conversion to APFS after once again having reformatted the SSD back to HFS Extended Journaled. It would appear that when looking through the Disk Utility app on the USB with macOS Sierra that APFS was on it's way but spewed out an error. The first look in the Terminal after my initial installation of macOS High Sierra yielded an error that I haven't written down. I remember that it failed to continue with the conversion. So now that this is all over and I'm on the release version of macOS Sierra 10.12.5 - what are my options for converting the filesystem to APFS when High Sierra rolls out in final form? My options are to wait and relax? I can do that. I just would like some input from other members that might have gone through the same as I.