I have two USB hard disks connected to my computer on which I keep photos, I usually keep them manually mirrored by copying the same stuff onto each but sometimes they get a little out of sync and I just manually copy my pictures folder over from my "working" drive now and again so that all the new stuff I've edited etc is kept on both drives, this material will only be a few files that I've missed. I just copy the complete folder over so I don't miss anything. I also keep one disk off site and swap it for the "live" backup disk now and again, so there are actually 3 disks in the rotation but that isn't important for the problem.
However, I'm getting somewhat strange behaviour in Win 10 when it comes to copying files from one disk to another.
For simplicity let's say I have a 1TB drive and 700GB of files in my photos directory. When I try to copy my photos directory from disk 1 to disk 2 it says it can't because there isn't enough space as there is only 300GB free.
Because the copy is an overwrite (i.e. I'm overwriting the photo directory and almost all of the actual image files) then I'd have expected the 700GB of new files to take up the same space as the 700GB of files they are overwriting, plus probably less than 1GB of new material. However, it looks like Win 10 needs twice 700GB in order to copy the files over and so wants there to be 1.4TB free on the destination before it will begin the copy.
Am I missing something really obvious here or is there a way around this behaviour so that I can overwrite 700GB of files without needing 700GB of free disk space before I can start?