Helping people with computers... one answer at a time.

The number of backups to keep is a personal decision, I give both my recommendation and my own strategy for backup storage.

I've received your newsletters for years and I can't count the ideas I've gotten from it. My question is this: How many complete hard drive backups should I keep on my external drive? My internal hard drive in my HP is 1 Terabyte, and my external drive is also the same. I use Acronis True Image software. Many thanks for all your ideas.

In this excerpt from Answercast #40, I look at the typical need for backups and outline my (overkill) strategy for my business.

How many backups?

There's actually no right answer for that.

The idea here is that if you keep backing up:

  • Eventually, you're going to accumulate a lot of backup images of your machine;

  • And eventually, you're going to run out of space.

The question of how many to keep is a difficult one to answer because it really depends on your own eventual needs and expectations for when you might actually need to use a backup. For some people, having a backup from six months ago may very well be important. For other people, not so much.

My recommendation

So, my recommendation for a minimum set of backups to keep (of full backups to keep) would be along the lines of:

  • Maybe two months worth.

I say that with the assumption that you're doing something like making a full backup once a month and then creating incremental backups every day during that month. So, at any point in time, you can go back up to two months and restore any files, folders, or even your entire system as of that date a month ago.

I always recommend that:

  • You at least keep two full images.

  • The current one, in other words, that one that was just made;

  • And the one prior to it – in case the one that was just made had some kind of problem.

Backup strategy

That's regardless of your timing, regardless of how you're actually doing your incremental backups between the two.

The assumption is that within the timeframe between one full backup and the next, you will discover whatever malware perhaps that may have gotten on to your machine. You will know to backup to something that you actually have.

  • That's kind of a rule of thumb. It's not really a hard and fast rule.

You can keep all you want

You may want to keep more. In fact, if you've got the hard drive space for it (if you can exceed what I've just described with the hard drive space you have on your external backup drive), there's absolutely nothing wrong with keeping more than you need.

You just never know. Maybe someday you will need it.

  • There's never anything wrong with keeping too many backups.

  • You can, however, run into problems by not having enough.

Which is why I use my "two full backups" rule as the minimum number of full backups that you want to keep at any point in time.

My strategy

As for myself, what I do is this.

I keep the full backup for the last quarter. In other words, three months worth of full backups. I keep the full backup then, that was taken at the beginning of each quarter: which means I will have, for example, January's and April's and July's and October available to me.

I keep those for about a year. Then once a year, I will save the backup that I took at the beginning of the year. So, I'll have machine images that go back to January 1st for the first of every year for the last x number of years; however long I've been backing up a particular machine.

That's me; that's overkill for most people. It has more to do with the way I want to run my business and my computers than it does with a normal person's actual requirements for data retention.

So those are the ideas that I come up with, like I said, if you need just a short answer:

  • Make sure to always keep at least two full-backups.

Article C5649 - August 2, 2012 « »

Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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Chris Calvert
August 3, 2012 1:57 PM

Coming from a city that has recently had several severe earthquakes I keep 4 copies. The 1st is the original, the 2nd on a workstation next to me, the 3rd is a separate building on the same property and the 4th in another city (about once a month). Often the problem isn't a corrupt drive or malware but in the event of something like an earthquake,although your data may be okay in that it physically survived the quake, you still can't access it because the authorities have refused you access because of potential danger. I have had secondhand experience of this dozens of times. Do not EVER make the mistake of thinking you will never need a backup.

August 3, 2012 8:20 PM

I like to make and keep one or 2 backups immediately after installing windows (and running Windows Update) and another after re-installing my basic applications. That way I can "reset to factory fresh" without having to reinstall ALL of the windows updates and my basic applications.

Your Jan 1st backup performs much the same function.

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