I am running 10.11 on my Mac Pro (mid 2010) and back up my SSD (250 gig) boot drive for that to an external USB3 1TB drive - If I wanted to try all the latest OS (Sierra, High Sierra, Mojave) could I just partition that drive and have all three on there to try out ? Presumably there would be loss of data ? Without a real faff of copying vast quantities of FLAC files from another drive its the only "spare" decent speed drive I have to play with.