Is Incremental really Incremental?

Discussion in 'Acronis True Image Product Line' started by sendmehere, Sep 24, 2005.

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  1. sendmehere

    sendmehere Registered Member

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    I have bought and used TI8 for some time, and I noticed a little problem recently...

    From day one, I started using Secure Zone to store the images, and I had created ONE full image, and a number of incremental backups from then on...

    But today, I noticed that the "incremental" doesn't really incremental, because I've checked my data volume about 10GB in total but the images used up about 25GB in total...

    Why is that?

    I thought all incrementals + full image = one complete image, is that still correct?



    Thanks in advance
     
  2. Menorcaman

    Menorcaman Retired Moderator

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    Hello sendmehere,

    I'm afraid it's not as straightforward as that. Assuming no compression, a full image would take up as much room as the Used Space on your source drive. Any incrementals created would then be cumulatively added on top of that.

    TI creates an image by taking a snapshot (thumbprint) of the sectors that are in use at the time and saves the data contained on the in-use sectors only. A thumbprint of those in-use sectors is also included in the image. Every time TI creates an incremental image, it compares the the thumprint contained in the previous image with the snapshot of the in-use sectors for the new image. It then only saves the data contained on those sectors that have changed since the previous image. So far so good.

    However, as you open and close applications (including Windows itself) or, more importantly, carry out disk defragmentation, the thumbprint of the current in-use sectors will have changed significantly since the previous image was created. So even though the files themselves may not have changed in size, with so many changed sectors, it's not unusual to find that an incremental turns out to be almost as large as the original full image. Hence, again assuming no compression, it could transpire that a full image + one incremental equals almost twice the Used Space of the source drive.

    Trust the above makes sense :)

    Regards
     
  3. sendmehere

    sendmehere Registered Member

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    Thanks so much for your reply, Menorcaman.

    Now I understand the concept...
    But the thing is, every time when I want to make some changes and do a backup, I would first restore my last image, then do the changes and then backup (this way I can be sure that things are "clean"), and for my recent changes, I just installed a new program, would that cause so much changes on the sectors? 'coz I know the most recent backup I got used up almost 7GB of space while the program that I installed used only 120MB, that's about 70 times the changes (file changes)...

    Would an installation of some 100MB causes changes of sectors on some GB of space?

    I just don't know what to do ....
    maybe I do a full backup instead .... even more effective than an incremental...

    Thanks.
     
  4. jmk94903

    jmk94903 Registered Member

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    At the same time as the installation, Windows is running and writing new files or rewriting old files. So, lots of things change, far more than the 100MB added to the drive. All the changes need to be included in the incremental, so it's large.

    Incrementals of data disks, as opposed to the boot disk with the operating system, are relatively small. Incrementals of the boot disk tend to be large.

    So, your idea of making only full system backups makes sense to me. That's what I do.
     
  5. sendmehere

    sendmehere Registered Member

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    Hmm... I see, thanks, jmk94903.
    I think I'll do full backups instead next time...
     
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