Those that know me well, know that if I had an actual religion it would be the Church of Backups. A place where all my data (encrypted with a private key) to go worship the coming of the great disk corruption of their platter or the solidification of their state to put it another way.
Which raises the questions: just how many backups, stored where, frequency, types, location do you actually need to sleep at night?
The answer is, of course, always N+1 where N is a number that greater than zero and equal to the number of backups you had when you last lost some data.
Every users situation is of course different and many articles and even books—I think— have been written on the subject.
The easiest answer that covers most users is at least two. One one-site and one off-site. If you can only do one, then make it off-site. The reason for the on-site backup is that it makes recovery quicker, generally easier and you have total control over the device - except that it will fail eventually, hence off-site (cloud) first.
Some things that shouldn't be considered as backups are: DropBox, GoogleDrive, iCloud (Desktop, Documents, Photos) or any other file sharing service that you use.
~~Should~~When your machine / disk dies having everything in the cloud with a file sharing service will help you. But when you accidentally delete a document / photo and don't notice until later, they won't and this is where we get into the difference between a backup of your current files / file synchronization and a backup archive - but not today.
Having once lost 3 months of work due to lack of a backup, I have never, ever lost a file since. My backup configuration is overkill for almost everyone, but there are parts that almost everyone could make use of depending on their needs:
- Time Machine Backup, net. drive, continuous
- Time Machine Backup, ext. drive, weekly
- SuperDuper Image backup, ext. drive, at least weekly
- Arq Backup, Wasbi (cloud service), continuous
- Arq Backup, ext. drive, continuous
- Arq Cloud Backup, Wasbi, continuous
- BackBlaze, Cloud backup, continuous
Yes, you counted them, my files are backed up up to 7 different ways - some are only backed up 3 different ways, it's complicated.
Is it overkill? Yes. Will I be removing some of them? Yes. Backblaze will probably be retired, leaving 6. Also, yes, I use iCloud Photos, Desktop & Documents, DropBox and whatever flavor of Google Drive is being pushed this week.
I have many Terabytes of data, most of which are not on my machine, all of which are backed up (multiple ways) and all of which are available to me should I need them - that's the advantage of cloud backup / archive but I've rambled on for too long already to go there. Maybe another day.