I run Sierra and iCloud Drive, and it seems not every file in the iCloud Drive folder is physically on my Mac. Sometimes it is clearly downloading the file when I try to open it. I haven't bothered to read up on the features of Sierra, but I assume it works similar to the the optimisation of Photos on my iPhone, where it also has to download photos sometimes when I try to open them. How do I backup this data? If I use e.g. Time Machine or SuperDuper!, how do they handle the new iCloud Drive? Will the software manually download all files and delete them? Will this cause the backup-process to take ages to complete?