Can file sync replace backup?

There’s a little battle going on between companies like Dropbox which are now claiming that they do “backup”, and backup companies like Backblaze saying that sync is no good for backup.

From a concept point of view, these are obviously totally different, but it’s interesting to consider how one concept might partially fulfill the purpose of the other.

I just added the following comment to Backblaze’s post, on the question of the extent to which sync can mimic backup:

– Sync services usually assume that all files being synced sit in a single folder on your machine (although Dropbox recently loosened this requirement). The disadvantage is that you can’t easily sync files in other places. The advantage is that, with the OS hook they typically provide, sync is incremental so when a file changes it’s uploaded immediately. With a backup service like Backblaze, it can take hours before a file is safely backed up.
– Backup services can usually include files on external drives. Fewer sync services can do this.
– Sync services don’t offer encryption using the client’s key; this is an option with backup services like Backblaze. It allows users to prevent the backup/sync service from accessing the contents of files (but means that if you lose your private key, your files are gone).
– Backup services let you restore all files as of a particular date. This makes it easier to recover from widespread corruptions, such as ransomware attacks.
– Some sync services offer versioning, but only on files that have not been deleted. I believe Google Drive is like this. So if you delete a file and empty the trash, it’s gone forever.
– You might think you can use a backup service to add security to your Google Drive, by syncing your cloud files to your local disk and running Backblaze on that. Sadly this won’t work because only regular files, and not Google app files (such as Google docs), are actually synced to local copies on disk.

And couldn’t resist adding this:
– Backblaze is a terrific service, but it has some frustrating design flaws which I hope will eventually be fixed. I use them as examples of various design principles in my recently published book…


I’ve just been through loss of a computer and restoration, after the main hard drive on my Mac failed.

Some of the stuff I got back I only was able to retrieve because files were on older backups than the very latest version (partly a mistake of mine and partly a side-effect of the way escalating drive errors caused backups to terminate early).

I’m pretty sure if I’d only been relying on a Dropbox-style sync, I’d have lost things and, worse, incurred a major amount of time trying to work out what I’d lost.