When I wrote “Apple’s File Provider Forces Mac Cloud Storage Changes” (10 March 2023), I closed the article by noting that backing up data in cloud storage services was potentially fraught because online-only files wouldn’t be backed up. I recommended downloading your entire cloud storage data store, at least temporarily, so it would all be included in your backup. New files you subsequently created would be local and thus backed up, but there are likely situations where files created or modified by collaborators would not be properly reflected in your backup.
That is, unless you’re using the most recent version of Carbon Copy Cloner, which can temporarily download cloud-only content, back it up locally, and evict it again to avoid consuming too much local space. Agen Schmitz mentioned this feature in his Watchlist item (see “Carbon Copy Cloner 6.1.7,” 11 September 2023), but I wanted to call it out more explicitly because it’s unusual and clever. Bombich Software explains:
When a file stored by one of these storage services is flagged to reside only online, the local copy of the file is deleted from your Mac and replaced with a 0-byte placeholder file. While this is a convenient feature that allows you to free up some space on your Mac, this feature imposes a logistical challenge to creating a local backup of those files. If you want to have a local backup of these cloud-only files, CCC must temporarily download these files to your startup disk. CCC can do this, but because this involves downloading a potentially large amount of data from the Internet, this functionality is disabled by default. Likewise, allowing this data to co-mingle with your startup disk’s backup could lead to a situation where it is impossible to restore your entire backup to the original disk due to space constraints. To avoid that, we recommend making backups of your cloud-only storage to a separate volume on your backup disk.
The page continues on to provide complete instructions and explain why some iCloud-only content still won’t be temporarily downloaded (because Apple isn’t yet using its own File Provider technology for iCloud, ironically), among other interesting technical details. It’s worth a read if you’re interested in quirky backup topics or the integration of local and cloud storage.
And, of course, if you’re highly concerned about maintaining local backups of cloud data, add Carbon Copy Cloner to your backup strategy.