Two tools that look alike
Cloud sync services and backup services both copy your files to another place, so it is easy to treat them as the same thing. They are built for different jobs. Sync aims to make several locations look identical. Backup aims to keep a recoverable history, so that you can go back to how things were.
The difference only shows up when something goes wrong, which is exactly when it matters.
What file syncing does
With file syncing, a folder on your computer is linked to a copy online, and often to copies on your other devices. When you change something in one place, the change is sent to the others. Edit a document on your laptop and the same edit appears on your phone. Create a file and it shows up everywhere.
The key word is mirror. Most cloud storage services work this way, and a synced folder is trying to be the same everywhere, all the time. That is very convenient for working across devices, but it means the system faithfully copies mistakes as well as improvements.
How a synced folder can lose files
Because sync copies every change, several kinds of problems spread instead of being contained:
- Deletion. If you delete a file on one device, the deletion is usually sent to the others and the online copy. Many services move the file to a trash area first, but that area is often limited in time or space.
- Overwriting. If you save a bad edit over a good document, the bad version replaces the good one everywhere.
- Corruption. If a file becomes damaged on one device, the damaged version may be uploaded over the healthy one.
- Malicious software. Ransomware encrypts files so you cannot open them. A sync client may treat the encrypted files as ordinary changes and upload them. Some services keep earlier versions that can help, but this varies and is not guaranteed.
- Accidental moves. Dragging a folder out of the synced location can look, to the service, like deleting it.
- Shared folders. If someone else with access removes files, they may be removed for you as well.
None of this means sync is a bad tool. It means that a second copy created by sync is a copy of your current state, not a safety net for your history.
What a backup does differently
A backup is meant to preserve files so they can be restored later. Typical features include:
- Version history. Older states of a file are kept, so you can recover last week’s version, not just today’s.
- Retention of deleted files. Items you remove from the source can stay in the backup for a set period or until you choose to purge them.
- Separation. The backup copy is not changed the instant you change the original, which limits how quickly a mistake can reach it.
- Restoration tools. You can usually restore a single file, a folder, or a whole device.
Some online services are sold as backup and behave this way; the benefits of a cloud backup depend on how long versions and deleted items are kept, so it is worth reading the retention terms. Others blur the line by adding version history to a sync product. The label on the product matters less than what it actually keeps and for how long.
A quick way to tell which you have
Ask a few questions of any tool you rely on:
- If I delete a file by accident today, can I get it back next month?
- If I save over a file, can I retrieve the previous version?
- If my account is compromised or my device is infected, are the older copies out of reach of the same problem?
- Is there a copy that does not change just because I changed the original?
If the honest answer to most of these is no, you have sync, not backup. That can be perfectly fine for convenience, as long as you know that a mirror protects against a lost device more than against a mistake.
Combining them sensibly
Many people use both. Sync keeps current work available on every device. A separate backup, whether an external drive that is not always connected or a service that keeps versions, provides the history. A common rule of thumb is to keep more than one copy of anything important and to keep at least one of them somewhere different from the original.
Backups need occasional checking too. A backup that has silently stopped running, or that you have never tried to restore from, offers less comfort than it seems to. Opening a few restored files from time to time is a simple way to find out whether it works.
No arrangement is perfect, and outcomes depend on the services, settings and habits involved. But knowing that sync copies changes while backup preserves the past will help you decide which files need which kind of protection.