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How long should I keep backups?

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In your books you suggest that we keep backups for 2 months, as an example. I feel very comfortable keeping no more than 3 days. Is there any drawback in using such a short time, or is it OK?

Ultimately, this is an unanswerable question in a general sense. By that, I mean three days might be enough… or it might not.

It actually depends on a number of factors that range from your comfort level to your risk tolerance, as well as your personal back-up scheme.

To understand how long you might want to keep backups, we’ll want to look at those risks.

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When in doubt

If you don’t want to put a lot of thought into it, I would absolutely fall back to my two-month recommendation. In slightly more detail, that means:

  • Perform monthly full image backups of your entire machine.
  • Perform daily incremental images building on those full image backups.
  • Keep backups for two months.

Without knowing more about your requirements, this represents a balance between recoverability – anything in the last two months can be recovered – and disk space – only two months’ worth need be kept.

It’s also what I do.

Implications of how long you keep backups

The key to understanding how long you want to keep backups is to understand exactly what happens after whatever time period you choose passes.

External Backup DriveIn your proposal, exactly what happens after three days? What’s lost?

Think of each backup as a representation of your computer “as it was” when the backup was taken. As a result:

  • Yesterday’s backup: everything on your machine as it was yesterday.
  • The day before yesterday’s backup: your machine as it was two days ago.
  • The day before that: your machine as it was three days ago.

Your machine as it was four days ago? Well, if you only keep backups for three days, then that backup was deleted to make space. Older versions of anything that changed in the three day window will be lost.

Let’s look at some examples of what that implies.

Malware

Let’s say your machine becomes infected with malware. As I’ve stated many times, restoring to a recent backup taken prior to the malware’s arrival is probably the fastest and most reliable way to completely remove it.

Ideally, you would notice quickly, and restore the previous day’s backup.

But… what happens if you fail to notice for, say, a week? Perhaps you don’t use your computer for a while. Maybe it takes a week to figure out that the odd behaviour you’re experiencing is, indeed, malware.

With only three days of backups, all you have is a backup of your machine as it was three days ago – after the malware arrived. That backup – in fact, all three backups you have – are infected. You no longer have a clean backup you can restore to.

Accidental deletion

Accidents happen, and sometimes we change our minds.

Let’s say on Monday you delete a file you believe you no longer need. You’re done with it, or so you think.

Then, later that week – perhaps Friday – you suddenly realize that not only were you not done with it, but it turns out to be critical.

With three backups, you have backups of your machine “as it was” on Thursday, on Wednesday, and on Tuesday. But not on Monday. As a result, you no longer have a back-up copy of the file you deleted: it’s gone.

File corruption

Either software or hardware can fail in such a way that a perfectly good file can be damaged so it can no longer be opened or used. The file may be present, but it contents are so much garbage.

As above, let’s say on Monday your computer experiences an unexpected power loss, and shuts down without warning.

Come Friday, you suddenly realize that a file you rely on to perform some end-of-week processing every Friday can no longer be opened – the application that tries to open it reports it as being broken, or of the wrong format. It looks like that power problem earlier in the week caused your hard disk to damage the file beyond repair.

Once again, with only three days of backups you have your machine “as it was” on Thursday, on Wednesday, and on Tuesday.; all after the damage had happened. You no longer have a backup copy of the undamaged file.

So, how long should you keep backups?

As I said, there’s no general rule I can apply that would make sense for everyone.

Clearly, the first few days are important. Things like lost files, malware and the like are often discovered very quickly, and typically you’ll need go back only a day or two when that’s the case. Of course, a sudden and total hard disk failure makes itself known quite quickly.

In situations like that, your three-day proposal is quite sufficient.

The questions I’d have you ask are:

  • How confident are you that you’ll discover whatever it is you might want from your backup within those three days?
  • What would be the cost – be it monetary, emotional, or just the time to re-create it – should you be unable to recover something because you didn’t discover you needed it before your three-day backup period passed?
  • Is there any reason you can’t just throw more disk space at it and increase the number?

I’m using your three-day proposal as my example here, but the questions apply for any time period you might choose to keep backups, be it three days, three months, or three years. For various reasons and in various situations, the proper retention period could be any of those, or even longer.

Ultimately, I can’t answer this question for you, but hopefully I’ve given you a few things to think about.

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15 comments on “How long should I keep backups?”

  1. If you are finished with the file but the file is still important to keep (financial records, legal records etc), make two “archival” backups. These backups are then kept in two areas that are disaster isolated from each other.

  2. I might be slightly OTT, but I keep backups forever. I only change my desktops when it dies, or cannot handle the software I want to use, for instance windows 98 with a Pentium 4 processor couldn’t handle superfast broadband, and I always keep the hard drive from the old computer (as far back as far as my IBM PC2) and use them for multiple backups. Cheap and simple! Also saves wiping the disc (either with software or a hammer) if I sell on the old PC – just drop a new cheap drive in it..

    • Keeping files forever is not the same as keeping backups forever. How many full backups do you do and how long to you keep them.
      If you edit a word document and a year later you find you didn’t like the edit, can you go back and get the old one?

    • For some contracts, basically my employing company theoretically would have had to retain Back-ups etc for at least 30 years – and that was from the agreed end of a Contract, which in itself, may be around 5 years after the physical delivery of the last item.

      It was a very moot point as to whether the company or the customer would have computers etc capable of handling the physical format of the back-ups, before even considering whether these would have survived without deterioration to the point of being unusable.

  3. In late Autumn of 2013, I discovered that in mid-July of 2013 a weird glitch pre-pended 16 null bytes to dozens of files on one of my external USB disks. Some of those files are still corrupted.
    I know when this happened, because the backups of early July 2013 have good files.
    I now have three copies on different disks of a folder named July-1-DO-NOT-DELETE, each of which contains 65GB of Macrium backup files. I retrieved a file from one of those folders eight days ago.

  4. Some types of companies need to keep files essentially forever. The furthest back I have had to go for my boss is 15 years – which made a friend of a company which was considering litigation.

    Last year we switched from tape backup to a hard drive mounted in another computer on the network. It runs five times as fast, costs a third as much and has a much longer probable read time. WD 2 TB “green” drives are our current choice for backups.

  5. I would keep system images longer than a year. I had an issue early this year that was finally resolved by restoring successive previous images, until I found one which, when Windows and all my software on that old image was updated, did not have the problem in question. However, restoring and updating several intermediate images did not resolve the problem. That particular instance was when Win8.1’s sfc started being unable to fix a supposedly corrupted system file, an issue that many had blamed on a particular Windows update, and which Microsoft had said was not “really” corruption. Other issues sometimes occur that, by themselves, may not bother you, but which, when you have an excuse to clean house, you fix them also.
    A goodly percentage of the programs we use get updated regularly, programs such as Adobe Air, Java, Quicktime, etc., as well as more specialty programs such as CCleaner, Copernic, Revo, etc. Updating an old image means updating such programs using the latest installers instead of successively installing the half-dozen or whatever updates that have occurred since you made the image in question. What that means is that you’re not compounding any errors. Updates inevitably get rid of bugs, some of which might have affected the rest of your system besides the functionality of just the software in question. In other words, maybe the June update of program X fixed a bug that was in the April update, and the September update fixed a couple of other bugs, and, by skipping all those intermediates, you might very well have a cleaner system.
    Sometimes an issue occurs regarding which you don’t know when the system was first affected. I rarely use bluetooth, for instance, so when I couldn’t connect via bluetooth recently, I had no idea how long the issue had been festering, but going back to more than two months ago resolved the issue, as well as fixing another issue in which Windows would not “remember” recent items that had been opened on my secondary internal drive. It remembered anything on the main internal drive just fine.
    It might also be helpful to save an older image for a restoration that you use simply to de-activate a particular program in order to re-install it. Adobe, for instance, is not always kind toward reinstalls, and if I were to decide to reinstall a version of Premiere Elements, which I gave up on a couple of years ago, the company might hassle me when I tried to reactivate the program. That might be more trouble than necessary in that particular instance, I don’t know, but it could be a useful last resort. In addition, with Macrium, you can browse older images, and you might discover files on them that cannot be obtained elsewhere. Since storage is cheap these days, I say save all the images you want., but two months is not nearly enough: you never know how far back you might have to go to fix a problem, for real.

  6. Dear Leo,

    I do so need to know how I can get my
    send page by email/ link back in my IE.
    I have window 10 and am not impressed.
    Please help, thank you.

    Respectfully,
    da6151

  7. I have a 5TB backup drive and a 3TB backup drive. I also keep other stuff on it. I keep backing up till I need more space and then manually delete a few older backups as I need space. I don’t see much reason on having a lot of empty space on the drive. May as well have the space filled with backups till I need the space for something else.

  8. Hi Leo, I heard that the 1s and 0s in pixels deteriorate over time, or some pixels die, is that true? If so, how can preserve my photos and videos? Could hardware damage also cause it?

    Thanks

    • The ones and zeros in pixels are stored exactly the same way as the ones and zeros of any other data on the storage device. If the pixels could fade, we’d be losing data all the time. Although, it is possible for data to be damaged, backing up regularly will protect against this. Back up early and back up often (at least daily).

      • Thanks Mark.

        I was asking because I saw a short thread where somebody said that over time a pixel can lose quality going from like 1 to -1.5 or -1.6, etc. So I guess it’s not true then

        So basically if I get hardware damage or wear and tear, it either opens a file looking exactly like it’s always looked, or it doesn’t open at all, right?

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