How long should I keep my backups?

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Summary: Having a regular backup in place is critical, but then what? We'll look at how long you might want to keep those backups and why.

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I'm going to expand on your question just a little bit and talk about backups in general as well, not just registry backups.

The answer is that it depends on the reason for your having made a backup in the first place.

Let's look at some of the reasons, and the implication on what's called "data retention".

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Some backups are made simply as a safety net prior to some risky event. For example, you might backup your registry, or your entire machine, just prior to installing some software that you don't completely trust. Registry backups (and System Restore Points) often fall into this category.

These types of backups are often temporary. Once you've convinced yourself that the risk has passed, and you're certain that you'll never have to revert to your backup, then there's typically no need to keep it.

That could be moments, hours, days or weeks, depending on just what it takes to feel confident that you'll never need to revert. Typically, it's closer to hours than it is to weeks, though.

Regular backups are a slightly different story.

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Some backups are configured to save exactly one copy - the most recent. In this case, you're not accumulating backups, but you only have the most recent to recover from. You're automatically discarding the prior each time you take a new backup.

More typical, and in my opinion more sensible, is a configuration where each backup is kept separately. If you're doing nightly backups at the end of a month you'll have 30 different backups you might be able to go back to, or extract files from.

There's no set answer as to how long you should keep these, as it really depends on your own configuration, your own needs and your own storage capacity. You might discard backups older than a week or a month or a year. You might decide to keep specific snapshots "just in case", but discard the majority.

As just one example, I keep a month's worth of daily incremental backups, three months of monthly full snapshots, each quarter's snapshot for a year, and then the snapshot taken on January 1 of each year for as long as I have space. At 70+ gigabytes for each monthly snapshot, the complication is worth it to manage the space.

As I said, that's just an example, and my needs might well be considered extraordinary compared to yours.

The rule of thumb is to simply think long and hard about "would I ever actually need anything from this backup ever again?" ... and then keep it a while longer.

But before answering that we also need to look at what's been backed up, and what the implications of "needing it again" might be.

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A complete system restore to a backup image resets everything on that machine to the condition it was in on the day that backup was taken. Everything since the time that backup was made is lost. As you can imagine, then, while I might very well restore to an image of a few days ago because of a system failure or other catastrophic event, I certainly won't be restoring my system to the image taken on January 1 two years ago.

I keep that image and others that I'd never fully restore to because of the files they contain. While I might never completely restore my entire machine to their contents, I can still use my backup software to explore and restore specific files from the backups taken on those earlier dates.

All that leads to an interesting observation about registry backups...

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I can't see using a two year old registry backup for anything. In fact, I have a hard time seeing a registry backup being used for anything after even a couple of weeks.

The issue is simply this: how would you use the registry backup? Likely you would restore it, in its entirety. The problem is that after even a few days your system may well have changed to the point where that backup simply doesn't make sense to restore anymore. Yes, you can examine a registry backup to determine what specific keys were set to what specific values, and if that's something you see yourself doing or needing, then you might keep the backups longer, but in general backups of only the registry are, by their nature, short term.

The best evidence is Windows own System Restore function, which is nothing more than a glorified registry backup. Based on disk space it keeps backups or "restore points" for only a few days until they're removed to make room for newer restore points.

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• How do I backup and restore the registry? "First backup the registry" is a common instruction when troubleshooting other problems. We look at three different ways to backup the registry.

• Can I recover from a virus by just restoring my registry? Viruses and other malware often work in part by making changes to your registry, so it's tempting to think that's all that needs to be restored. It's not.

• What backup program should I use? Backing up your computer's data is critical. What program should you use? There are many, but the best is which ever one you actually will use.

Article C3644 - February 8, 2009