Solved Macrium Reflect Free - Odd image size?

Macrium Reflect Free v8.0.7783

I create new Differential images weekly and, for the first time today I saw that the created Diff image is smaller than the previous Diff image of 1-week ago? I have been using my computer every day and I understood that Differential images always increased in size as time went on due to more changes happening relative to the original 'Full' backup. There have been app updates as well as new user files created.

To be sure it was not a one-off anomaly I created a second Diff image and it was the same? I checked the MR logs in case I had made a mistake but I hadn't. See photo of my image records.
I did not think this was possible since there have been more changes in the 7-day period in-between compared with the Full image.

Has anyone else had this happen? Can anyone explain how this might have happened?

The differential is a reflectiion of data that has changed since the last FULL backup. If you continue to add new data, then each differential will grow in size. However, if you delete data that was present in previous differential backups, there may be less to backup now, thus, a smaller differential.

Also, newer DATA may have been much more compressible.

Froggie said:

Also, newer DATA may have been much more compressible.

Click to expand...

But bear in mind that newer data won't make previous data any more compressible, so it would still be growing in size. The only way a differential would ever shrink in size is if there was actually less data to backup as a result of blocks being removed.

I just created a new Restore Point which made it the 8th one.
In between clicking the create and successful , the two last ones were
deleted. The folder was 17 GB and now it's 12.5 GB. Could this account
for the difference?

Flashorn said:

I just created a new Restore Point which made it the 8th one.
In between clicking the create and successful , the two last ones were
deleted. The folder was 17 GB and now it's 12.5 GB. Could this account
for the difference?

Click to expand...

Sure. While you provide no details on what type of backups you have and your retention policies, it is certainly possible.

hsehestedt said:

Sure. While you provide no details on what type of backups you have and your retention policies, it is certainly possible.

Click to expand...

Not for me but for @wiganken . Could this account for his discrepancies?

Flashorn said:

Not for me but for @wiganken . Could this account for his discrepancies?

Click to expand...

Once again, the only way a newer differential will be smaller is if blocks that were previously occupied have been deleted. Let's use an example to make this clear...

You create a full image backup of your drive.

You now add a bunch of files to the drive totaling 20 GB. If you now take a differential backup, you would be backing up 20GB of data. The actual backup may be smaller due to compression.

Now you delete 10GB of that 20GB of data that you added previously. You take a differential backup. SINCE THE FULL BACKUP you now only have 10GB of changed data (the 20GB you added minus the 10GB you deleted). This means that the differential backup only needs to backup 10GB of data rather than the 20GB it had to backup the last time.

Note that this is true only of data added to the drive AFTER the full backup was taken because the differential is only concerned with changes made AFTER that full backup was created.

Does this help?

@hsehestedt - Yes that helps me to understand how it may have happened. The only thing is that I can't remember deleting anything in the last 7-days (since previous image) to explain it. What is even more odd is that the amount of data I would have had to delete to offset the 'usual' increase would have to be around 2 to 3 GB and I certainly can't remember deleting that amount of data. I thought I would remember deleting that large an amount. I may have defragmented the SSD but I don't see that as accounting for 2 to 3GB of data.

@Flashorn - I have system restore disabled (since I use Macrium Reflect) and have no Restore Points. See photo.

I'll just have to accept that I must have deleted a block of data that was present in previous image but can't remember doing so. I'm getting old but what made me ask the question is that this is the first time this has happened in the 5-years I have been using MR. In the past Diff images have always increased in size.

I have looked into this some more and it seems that differential images should always be larger than the previous image so it seems like a glitch to me. I hope the next differential image is larger or else I will be wondering if MR has become unreliable.
In fact, I think I will start again with a new 'Full' image since I am not sure I can trust this last 'Diff' image.
See @Bree post: -

See my differential backups below, mine aren't always bigger....

@OldNavy - It's interesting to see someone else has the same issue but even Macrium Knowledgebase states that Differential image sizes should always grow in size. I have started again with a new 'Full' image: -

@OldNavy - Regarding your photo showing image list: - Is that from your MR log file or are you actually storing that many 'Diff' images? If you are storing them I suggest you create a new 'Full' image and delete all previous images. You will regain 65 GB of disk space.

To keep things simple I set retention rules to store 1-'Full' image and only 2-'Diff' images

wiganken,
I'm not sure it is an issue. It could be something as simple as clearing my browser cache which could be 1 or 2 GB's.
My backup regime is to make a full image every second Sunday and differentials in between. I keep 3 sets as an archive as disk space is not a problem.
I've never had a restore failure.