One of the dumbest aspects of downloading Xilinx tools is that you can spend hours downloading 100GB of tools only for the installation to silently fail at the end because you didn't install ncurses5. Now this might not sound too bad, let me tell you that the installer is doing an in-place installation, which deletes itself upon cancellation, so if you cancel the installation you will end up with neither the downloaded files nor the installed files. You're expected to download the 100GB again and hope for the best.
If you ever get the funny idea of downloading the offline installer, you'll run into the same problem. The installer moves its unpacked files into the installation folder, deleting the original installer. So if you have to do any sort of trial and error, you actually need 200GB of disk space. Once for the installer and once for the backup of the installer.