I’m going to come right out and say that Dropbox is not a sufficient backup. If all you have are files in a Dropbox folder that are synced to the cloud, you should not consider your files to be backed up and safe. This because your files are now entirely dependent on a company’s business model, one of the main perils of cloud storage, but also because synced cloud storage is not a true backup.
The reason Dropbox is not a good backup relates to how different cloud storage services work and the Rule of 3. The Rule of 3 states that you should have 3 copies of your data, 2 onsite and 1 offsite, for safest storage. The crux of the issue is that services like Dropbox, Box Sync, and OneDrive were designed to provide easy access to content from multiple locations and not to provide dedicated offsite backup. Because your files are synchronized across multiple locations, you really have one “copy” of the data that lives in both the cloud and locally. This is not enough to satisfy the Rule of 3.
With syncing, the method of creation and destruction matters – namely, when you update a file in one location it gets updated universally. Likewise, when you delete a file on your local Dropbox folder, it gets deleted in the cloud and vice versa. So if you are using synced storage and something happens to your local device, there is a chance your synced files in the cloud are at risk. And if Dropbox accidentally loses data in the cloud, as happened with cloud storage provider Dedoose, your local data are at risk.
I wish I could say that this is all theoretical, but people using synced cloud storage have lost data. For example, one researcher lost 8,000 photos both locally and in the cloud after a syncing glitch in Dropbox. Another person lost all his Box files when Box.com rolled his account into an unrelated corporate account. The good news is that synced storage services like Box and Dropbox do hold on to deleted files for 30 days, but this is not always foolproof.
So what should you do to make your data safer in this case? Add a backup to this system. Put a copy of your data on a local hard drive in addition to storing it in Dropbox. Alternatively, you can use a cloud storage service that provides independent storage/backup. For example, I use SpiderOak as an offsite backup. SpiderOak monitors my local files and saves a new version of a file to the cloud whenever I update it. This process is automatic, just like with syncing, but my cloud copy is independent of my local copy. If I delete a local file, the copy in the cloud is unaffected and vice versa. This means my cloud storage provides a true offsite backup and I’m more likely to get my files back if something catastrophic happens locally to my computer.
Cloud storage is a wonderful development in terms of convenience and providing offsite backup or access, but you should never rely on the cloud alone. It’s always best to follow the Rule of 3 and get another backup for your data, just in case.