Received this email from Dropbox today. I would have expected iCloud to download fully prior to moving a file to Dropbox or at least to have reported an error if the operation wasn’t completed. Thankfully the two files, both very large multi-gigabyte images, were also on my main photos drive and the backup. I had moved them off my Desktop and into a folder on Dropbox.
We’re reaching out because we’ve detected one or more .iCloud placeholder files in your Dropbox. These placeholder files could lead to data loss if no action is taken, as the recent release of macOS Sierra has changed the way Dropbox is able to sync files in some circumstances.
To make sure all your files are safe, please follow these steps:
Search for .iCloud files on Dropbox. Using the search bar on dropbox.com, type in .iCloud to see which files in your Dropbox are affected. When you’ve identified those files, you’ll need to recover the actual versions from iCloud (follow Apple’s instructions here).
Update to the latest version of the Dropbox desktop client (version 11.4.22). To ensure Dropbox continues to sync properly, download the latest version of the desktop client.
Manage warning notifications. You may see warning notifications from iCloud when you move files from an iCloud-synced folder into Dropbox. You can opt out of these notifications by following these steps.
Why is this happening?
The .iCloud file type is a “placeholder file” created by iCloud when it tries to free up disk space on Mac devices, as part of Apple’s new Optimize Storage feature. Placeholder files take up very little disk space because they don’t have any of the information that makes up the actual file. You can think of a placeholder file as a map to the actual file—the placeholder file lives on your device, while the actual file it represents lives on the iCloud server.
Unfortunately, moving .iCloud files into Dropbox can cause some serious issues. iCloud treats the file move as a deletion from iCloud, and it deletes the actual file on the iCloud server. In some cases, iCloud will move only the placeholder file into Dropbox, so Dropbox will sync that placeholder instead of your actual file. In this scenario, neither Dropbox nor iCloud still has the actual file.
This scenario can also occur if you’ve moved your Dropbox to a location synced by iCloud (like Documents or Desktop), or if you have a symlink to Dropbox in one of those locations.
For more information on Dropbox and iCloud on macOS Sierra, visit our help center.
The Dropbox Team