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File-based backup (differential) includes files that have not been changed

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I've only been using ATI 2014 Premium for a few days and I've noticed the following:
The file-based differential backup job that I created has a full size of about 3GB. Then the differential backups are about 200MB each for the past 3 days. What's surprising is that in these past 3 days I have been working only on a single excel file, which is about 50KB in size, i.e. I changed no other files and no system files are included in the backup (only my data files included).

I thought that I understood well the functioning of incremental and differential backups, but obviously I'm missing something important here; I just cannot comprehend how the changes in a 50KB file, produced a 200MB backup!

Moreover, when I click on More Features/Explore all backups/Files and Folders and then a select a file and click view versions, I see that there is a version for each file listed for every day that a backup was taken, although no changes were made to the file. This seems kind of odd.

I want to know why I'm getting the above behavior, especially getting a seemingly huge backup for changing only a 50KB file.

I want to emphasize that this is not a sector-based backup, and that I'm positive that there are no hidden or other files mistakenly included in the backup.

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I am having the same issues on ATI 2013 but my differential (and I tried incremental) backups are 4GB when I run a diff straight after a full backup and the machine has been sitting idle.

Pako,

How many pages are there to your Excel file? True Image will resave all pages even if you only altered one of many. In this instance the only difference between an incremental and a differential is that with an incremental all the pages will be resaved and a diff will resave all pages except the initial page.

It is quite possible if you have Windows indexing switched on that there are other background files that are being altered and for example anything with a database such as Windows Mail or similar will change in size as will AV and firewall databases, though I appreciate most people other than me have those on their OS partition.

Windows does an awful lot of writing and file buffer flushing in the background.

Hi Colin,

Thanks for the response. The Excel file has 24 worksheets, and the file size on disk is 60KB. I think that even if the whole file is re-saved, there is a huge difference between the 60 KB file size of the changed data and the 270MB of last night's backup. As you thought, I have email, AV and firewall files on the system drive C: (for which I have taken a disk image backup), and all my data for this file-based backup are on drive D:.

Apparently all files, even unchanged ones, seem to be in every backup version (in some form or other). I suspect that ATI places some information in every backup version for all the files in the backup, i.e. probably to mark files as unchanged, as well as store the changes of changed files. Do you think there could be any truth in that?

I expect that even if no files had changed, there will be a certain minimum size to any incremental or differential backup, required in creating the .tib archive. This minimum size would be the "cost" of creating any .tib archive. I don't know what that minimum is, and it's just my theory, but it seems reasonable.

Let's not forget that TI is a backup of used disk sectors. This may be a factor.

Hi tuttle and thanks for the response. What you are saying is quite reasonable and seems to be inline with my suspicion that ATI "makes a note" of the state of all the files in the backup, even the unchanged ones. That would require a certain minimum size for the backup, which I guess would be proportional to the size of the full backup.

GroverH thanks for the response. Although what you are saying could be a factor, cause I really don't know for sure what causes this, I would argue that if my problem was a disk-based based backup (i.e. sector based) then for sure it would be a factor. However, my problem is with file-based backup and I'm not so sure that amount of used disk sectors could be causing the difference between 60KB and 275MB. In any case, I have turned off auto-defrag, which is known to cause backup size issues with disk-based backups, to see if it also affects my backups.