Duplicate files in iCloud Drive; one of them has a download symbol next to it; why?

I copied large amount of data into my iCloud Drive on my iMac and then did the same on my Macbook Air hoping that this would save time uploading to the cloud. But now it's been days and only 10Gbytes of data have been synced. I am also getting duplicate files on my iCloud Drive. Some files have a download symbol next to them. Is this normal?