One of our competitors has been making a lot of noise recently about how they do “non-destructive restores”, meaning they don’t overwrite existing data when restoring old data from backup. Which is great, as far as that goes. We do restores in exactly the same way. In fact I don’t know of any backup products that don’t do restore this way.
But I think it’s worth pointing out that even though all Google Apps backup products restore data non-destructively, they differ significantly in how they back up that data in the first place.
When we originally designed Spanning Backup, we started with a guiding principle: don’t lose anything. This may sound obvious, but it’s a fundamental difference between us and the competition. Spanning Backup backs up your Google Apps data automatically every day1, and if it’s changed since the previous day’s backup, stores an additional copy. If it hasn’t changed, it stores that fact too.
non-destructive backups and restores
The result is a historical record of your data with daily snapshots. To be clear: Spanning Backup never overwrites older backups with newer data. You can always restore any historical snapshot. Other systems take a different approach, and overwrite previous backups with the most current data.2
Let’s take a look at a couple of common scenarios where this difference is acutely important.
If you sync your Google calendars or contacts with mobile devices or other applications, chances are you’ve encountered sync-related data corruption, or that you will. And when data becomes corrupted in one place the corruption quickly syncs everywhere, causing corrupt data to be backed up.
Similarly, let’s say you open Google Docs one morning only to discover that your documents still exist but all of your collections are missing. Your documents and collections have been backed up for the day, so the backup is missing all collection information.
In both of these cases, the difference between destructive and non-destructive backups becomes immediately apparent. If your backup system has been backing up your data non-destructively, recovering from these situations is simple: you just restore from a known-good snapshot, delete the corrupted data, and get on with your life. This is how Spanning Backup works.
But if your backup system overwrites yesterday’s backups with today’s corrupted data, you’re out of luck. Your one and only “backup” copy of your data has been corrupted. Frankly, we don’t consider this to be “backup” in any meaningful sense.
These issues are subtle but important to understand, and can have a dramatic impact on how well your backup solution works when you need it most. We welcome any questions or comments, whether in the comments section below or via email at firstname.lastname@example.org.
1 You can also perform on-demand backups with Spanning Backup at any time.
2 One competitor recently started retaining historical versions of document backups, which is certainly a step in the right direction. But unfortunately all of the document backups they made before introducing that change have been permanently lost. And since they still perform destructive backups of calendars and contacts, that data is still overwritten every day.