My plan was to move all my files which are stored in Dropbox to iCloud Drive. I tried 2 apps for accessing through the iPhone: - Documents by Readdle - GoodReader If i start to test the sync between the iPhone and OS X Yosemite (with copying a few files in the iCloud Drive through the OS X Finder), the sync works very well. I'm able to edit or delete files on my Mac or on the iPhone and after some seconds, i can see the change on the respective device. But after i copy my whole Dropbox files (around 4 GB) in the iCloud Drive folder and waited until all files are uploaded, the sync suddenly starts to be confused: Files doesn't appear on the iPhone or uploading of files (for example a picture taken with the iPhone) ends in a never-ending upload. I could reproduce this with Documents by Readdle and GoodReader. Sometimes both apps crashing when the never-ending upload occurs. I think that the sync of the iCloud Drive between 2 Macs could works well, but if you an iOS device to accessing files in the iCloud Drive this seems to be very unstable.