Hi, I have installed Dragonfly BSD in dualboot (that's with GPT and on EFI) recently, so it is possible.
> Slice the hard drive in two GPT slices using gpt (e.g., da0 and da1) As far as I know it would be da0s0 and da0s1 instead. (https://www.dragonflybsd.org/~labthug/handbook/disk-organization.html) > Create a, b, and d disklabel partitions on the Dragonfly slice (da0s0 > or s1) I haven't tried doing it that way. Instead, I did it the traditional way-that is having 3 gpt partitions/slices for boot, swap and root. Note that if you are going to do it the way I did it, then you have to bypass HAMMER2 auto completion (adding @DATA, @ROOT to the end) mechanism in /boot/loader.conf. After you have partitioned your disk, you just have to copy system from USB drive to your disk (consult handbook and replace /etc with /etc.hdd or just read https://gist.github.com/liweitianux/16161c9a3ca06d430c3d7e226033972e#copy-system-files). I believe that installation menu will still be looking for whole disk, so it's useless in your situation. After you copied all the things you also need to add an entry to your bootloader, /boot/boot1.efi is the file that's to be copied, consult documentation of your bootloader for more information on that. Then just continue doing what you need like with normal installation, remember to set password! I hope I didn't forget anything, have fun. magik
