[Apple] What makes Time Machine necessary if using iCloud?
Solution 1:
Time Machine can, in theory, restore the exact state of your Mac at any time. All apps, prefs, settings, documents.
iCloud will restore only your documents. Everything else would need to be re-installed from scratch.
Whether or not you consider that 'necessary' is your call.
Solution 2:
Yes Time Machine is needed even if you have iCloud. iCloud is not a backup system it is synchronisation.
Time Machine makes a copy of your file so it is in two places and if you delete one then the other is still there
iCloud makes the file available in several places but if you delete it in one then it is deleted in all places.
Also Time Machine copies all files on your disk and iCloud only syncs a few folders.
Solution 3:
The key is the difference between a copy and a backup.
iCloud Drive is essentially an off-site copy of your data. That’s great — if your house burns down, you still have your files.
But it is not a backup of your data. Because if you were to (accidentally) delete a file from your iCloud Drive and then immediately have your house burn down, the file has gone forever.
The main property that backups have that a copy does not is that they can go back through time. Let’s say you edit really important file.txt and make a terrible mistake, but you don’t realise for a while what you’ve done. Next week you open it up and realise your mistake.
iCloud Drive doesn’t help you here: the mistake you made has synchronised to the cloud. But your backup has a version of the previous file that you should — depending on available space and your defined backup rotation scheme — be able to go back and retrieve.
Similarly in the case where you deleted a file and then your house burnt down, a backup that didn’t burn down along with the house will allow you to retrieve that file. (Point 4 below solves for this disaster. You could also store your Time Machine drive in the shed, at work, etc.)
Ideally you should combine these technologies. The maximally ideal state is one where you end up with:
- A ‘local’ copy of your files that you work on every day. This is just your Mac.
- An off-site synchronised copy of your files that you can retrieve very quickly if your Mac is offline, or that you can use for convenience, e.g. accessing your files from your iPad. This is iCloud Drive.
- A local backup of your files that you can use to restore from very quickly. This is Time Machine.
- An off-site backup of your files that you can use when your life goes terribly, terribly wrong. This is the ultimate insurance policy; you hope you’ll never actually need to use this. Something like Backblaze.
Solution 4:
When planning your backup, you should always think about the worst-case scenario, and Time Machine can definitely fail (here's just one example among many).
Time Machine doesn't contain a clone of your system. It merely hopes to be able to restore a clone of your system, by applying incremental backups one after the other and by juggling with non-standard hard-links for folders.
So iCloud + Time Machine is not a sufficient, reliable backup strategy. You should have a real clone on an external drive, and this drive shouldn't be in the same location as your computer and Time Machine drive. (See 3-2-1 rule)
One advantage of using a complete clone (e.g. with Carbon Copy Cloner, among others) is that you can boot from it and check if everything works fine. With Time Machine, you typically only run a restore when you really need it.