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Can I just keep making incremental backups after I’ve made a full image backup?

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Leo, I’m using a shareware backup utility called AISL backup, which seems similar to Macrium Reflect that you recommend. Here’s the question. I made a disk image backup and every day I add an incremental backup. I’ve been doing this for about a year and so now have 300 plus files in the backup. Can I keep doing this? Or is it bad practice? I notice that somewhere you can recommended a full image backup once a week and an incremental in-between.

Nope, it’s not practical and to be blunt, it’s downright dangerous.

Let me explain why that is and what I recommend you do instead.

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Full versus incremental

Let me quickly review: a full backup is a backup of everything, period. It’s a snapshot of whatever it is you’re backing up. So if you’re doing a full backup of your drive, it’s a complete copy of everything on that drive. An incremental backup, on the other hand, is a backup of everything that changed since the last backup.

Let’s say, for example, you do a full backup on Monday; then on Tuesday you do an incremental backup, which will contain only those files that changed between Monday and Tuesday. Then on Wednesday, you do an incremental backup again. This time it will contain only the changes that occurred between Tuesday and Wednesday. You get the idea.

What you’ve done is exactly that, except you’ve repeated it 365 times in a row. Rather than copying everything, everyday, you’re only backing up a smaller subset: the things that changed. It is faster and it does take up less disk space overall. I do recommend that you do it; I just don’t recommend that you do it for as long as you have.

House of CardsThe risk

Here’s the problem: the incremental backups all rely on all of the preceding incremental backups. If any of the incremental backups are lost or damaged somehow, then all of the incremental backups that were taken thereafter are no longer valid. Each one depends on all of those that have been taken prior.

In a sense, it’s a house of cards. Lose the wrong one, and it could all come tumbling down.

So, for example, you take a full backup on January 1. You take a year’s worth of incremental backups, so you’ve got 364 of them (365 is of course the full backup). If you lose the incremental backup that was taken on, say, February 1st, then you’ll have lost access to everything that was backed up for the rest of the year.

Compromise

My recommendation is a compromise; take a full backup about once a month, then do incremental backups every day. That’s exactly what I do.

If you do that for a year, that’s going to take up more disk space than the one full backup and 364 incrementals that you have now. So you’ll need to manage your disk space somehow.

A full backup and the incrementals that follow it are what I’m going to call a “backup set”. I keep two backup sets. Set #1 is the current one: the full backup and then any incremental backups that are currently being added to it for the month that I’m in. Set #2 is the previous month: the previous month’s full backup and then all 28, 29, 30, or 31 incremental backups that were taken that month.

Occasionally, I’ll actually squirrel away one of the monthly full backups, but that’s more of an archival thing than an actual backup thing.

To sum up, things are kind of risky with your one year’s worth of incrementals. Everything could work just fine. But to be honest, I’d really encourage you to change your approach.

20 comments on “Can I just keep making incremental backups after I’ve made a full image backup?”

  1. Interesting coincidence. I was thinking of asking a similar question. In my case, I created a full backup after using the factory restore partition of my computer last April. I created an incremental once a month, so now I have a full and 8 incrementals. This January I made a new full backup.

    After a couple months, if I don’t find a need to retrieve a file from the first backup set, is there any point in keeping those incrementals? I’m thinking of deleting the incrementals and keeping the original full backup, the new full backup, and the monthly incrementals that I make following the new full backup.

    • That should work with most backup programs. I’d check the documentation or experiment by copying the incrementals to another location, before wiping them out. But do you think a backup once a month is sufficient. The question to ask yourself is, “Am I OK with losing 30 days of work.”

      • Yeah, I’m OK with once a month. There’s not a whole lot that changes from day to day with the exception of email, and even then, most email is not saved anyway.

        All backup strategies are a balancing act between risk and effort. As Leo says, if it’s in one place it’s not backed up. I extend that to include the physical location of the backup. If the backup drive sits next to the PC and someone steals my PC, they’re likely to take the backup drive at the same time. Therefore, all my backup would do is to protect against corruption, accidental deletion, etc. So I choose not to leave my backup drive connected but rather hidden in a closet.

        It’s a bit more effort to pull out the drive once a month and run the backup on the desktop and laptop, but based on past experience, I can accept the risk of only backing up monthly and I believe I’ve got a measure of protection against theft an flood (I know, fire is not a consideration in this).

        My question wasn’t really about would it work software wise, but rather was there anything that I was overlooking in adopting this strategy of deleting last year’s incrementals, once I deem the risk of having to recover something from them as low. I figure that if in the future I can’t access the recovery partition, I would still have the original full backup (if I needed to go back that far), But in reality, if I had to recover something, it would most likely be accessible in the current year full or incrementals. I just want to make sure I haven’t overlooked something in my thinking.

        • From a safety point of view, wiping out all of your incrementals sounds reasonable, with one extra step I’d recommend. I’d copy the incrementals I planned to back up to another location before performing the backup. Otherwise all of those incremental files would not be backed up during the time of the backup. It might sound picky, but really, you never know what might go wrong.

    • Sounds like what you’re doing is similar to what I do. I keep the incrementals only for a couple of months. I keep some of the fulls for a while. A full backup can always stand on its own, but reflects only the state of the machine on the day it was created.

  2. Don’t forget about differential backups which back up ALL the files that were changed since the last full backup; and you only need the last full backup and the differential tape for restores: not all the tapes in between. Much less a house of cards than incremental backups.

  3. When I was first learning to program in Basic at BBN, Basic would save a copy of all saved programs giving each save a new version number. The had a special delete command called delver which deleted all copies except for the first, the last and the second last version. This has become my persona backup rule of thumb. I have the first version, the one I created when I set up my computer and cleaned the crapware, my previous backup and the one that is in progress. In addition, I copy the latest to a 2.5″ HDD monthly which I keep at work.

  4. I use a strategy very similar to your recommendation except that I have 2 sets of backup disks. My incrementals fill one of the disks after about one month. I then bring home from work my second pair of disks, wipe them and start a new backup sequence on those. I take the recently used disks to work (off site backup) until the cycle repeats again. I an using pairs of disks because a single 1TB disk is not big enough. I backup video to one disk and everything else to the other. I like to use USB powered portable disks for convenience; plug them in and they work – but currently limited to 1TB. The video backup is weekly and the ‘everything else’ backup is daily.

  5. Here is my strategy, and I appreciate comments in case I am missing something. I do a complete system image periodically. I put all of my data files, which includes my email files, favorites, TrueCrypt containers and other stuff that may be located in various places when a program is initially installed, into one directory. I do a full backup of that folder every night, and keep the last three. If I ever have a problem, all I have to do is restore the one backup, or, if necessary, the system image and one backup. I have found it necessary to do this several times over the years, and it works great!

  6. I forgot to mention, In addition to having a backup drive locally, my son has a copy of my backups at his house, and I also copy the backups to thumb drives that I take with me when I leave the house. The system image – Vista – fits on a 32gb thumb drive, and my data backup fits on a 16gb thumb drive.

  7. I use differential exclusively, starting from a monthly full.
    I alternate the differentials between two 1TB disks, and copy the latest differential to a third disk weekly. It’s good to have old backups (several months), in case your files go bad, and you have to reach back earlier than a series of bad backups – which I have done!

  8. All the incremental, diff. etc terminology of backup really confused me a lot and the vital question how reliable are backup software that are available in market is there any lab or independent organisation which rate backup softwares like “AV-TEST” for anti virus softwares?

  9. I have read every tutorial on Backing Up written by Leo for a few years now but am still a little confused as to the best course of action in my situation after a system’s crash.

    I should add that I have had three complete systems failure within the past 18 months all of which may have been BIOS related and re-installing with Windows installation disc (not recovery) always carried forward either a new or pre-existing problem making me think that the installation disc had become corrupted.

    On Leo’s advice I have downloaded Macrium Reflect for the sole purpose of making a backup image or clone of the hard drive BECAUSE, as I have continuous backup files and documents to an external drive, this would be of no help to me when trying to rescue the situation using one of the well-known names because every time I tried to bootup on the previous three occasions I could not even in ‘safe’ mode.

    So, in my case my startup system ( I believe my Registry was probably damaged before as well) is what I am trying to protect.

    What I cannot find from all of the literature is – WHAT HAPPENS NEXT after a system’s crash?
    How is Macrium’s image backup applied to the hard drive to get things back to normal assuming that the drive has not been damaged if, as in my case, the OS disc is suspect?

    The crashes were caused by the deletion of a hidden and unwanted ‘piggy-back’ program, AVGs
    2013 update and then a continuous loop ‘Your computer is being Restarted’ blue screen.

    • BaliRob, I share your pain on the “WHAT HAPPENS NEXT” issue. I failed to restore my computer from my Macrium reflect Rescue Media, but when I got it fixed otherwise, thankfully I was able to restore all the files from an online backup which I use as part of my overall backup strategy.

      • @Tony2,

        Thank you so much for your contribution identifying with my problem. I feel that I have become expert at many aspects of computing whilst trying to learn from others on Google Search but when I put it all together it never seems to count for a ‘can of beans’ when wanting to return my desktop to perfect working order. I presently am
        using my aging Acer laptop and am desperate to clone it before that too lets me down.
        Wish me luck.

  10. I get your logic for backing up PC’s, however; what about large companies that have critical data? Do you still advise that monthly full backups with incremental backups in between still okay? I come from the a corporate methodology of doing weekly full backups and incremental backups in between. At the new company I am at they currently do monthly full backups and incremental backups in between.

    Is this considered good practice for company’s that have large amounts of critical data being backed up in case they have a disaster and need to recovery critical data?

    • Large companies with critical data really need a more comprehensive plan that covers all aspects of their business. Daily might not be enough, for example. I can’t really generalize a suggestion because different business needs would drive different requirements.

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