HOW TO AVOID BACKUP BLOWOUTS BY DISABLING iCLOUD OPTIMIZED STORAGE ON YOUR MAC
In macOS you can choose to optimize your usage of local storage by having your Mac automatically offload files it is already syncing to iCloud Drive, iCloud Photos, and other services. The logic is that you might have limited local storage and dozens to hundreds of gigabytes of data you don’t need access to all the time, such as filed documents and photos from years past. You want them available on demand—with an active internet connection—but not necessarily filling your drive.
However, there’s a big catch: So-called optimized files are backed up only in iCloud. Because there’s only a local placeholder for the synced file, Time Machine, third-party sync and backup software, and internet-hosted backup services cannot make copies.
You might decide that’s OK! You trust the integrity of Apple’s data centers and the quality of their operations. While Apple doesn’t offer insight into how it protects your data, it’s definitely the case that the copy has multiple copies of your data stored in three or more different locations to avoid
