Why Comodo Does Incremental Backup When It's Setup for Differential?

You can check attached screenshot where you will see it creates differential backup. But it’s nothing like differential because what was initial size ~60GB is now ~334GB :o

Why is that?

[attachment deleted by admin]

I’m not sure why you say Comodo is doing an incremental backup. The log indicates it is a differential backup. Is it because of the “incremental depth” comment in the log?

A differential backup copies all the files that have changed since the full backup each time a differential backup is run. The log indicates differential “snapshot 5” so all the changed files have been backed up six times – the full backup plus five differential backups. Do you have a lot of files that have changed since the full backup that could account for the backup file size increase?


I see that compared to EaseUS Todo Backup that keeps all differential backups outside of full backup, Comodo keeps all of them inside full backup but then why in addition to full backup 80GBs all 7 differential backups from EaseUs Todo Backup are sized from 6 to 10GBs each when Comodo full backup with differentials exceeds 350GBs?

There were few changes between backup routines which I do weekly so size difference that Comodo shows compared to EaseUS Todo Backup does not make sense.

All backups begin with a base (full) backup of the target data.


  • backs up only data changed since the last incremental
  • are smaller
  • take longer to restore because the base then all Incremental backups need to be processed, in order


  • backs up all the data changed since the base was created
  • are bigger
  • restore faster because the base and only the last Differential needs to be processed.

I believe that you can specify the base and also give a name to the Incremental or Differential backup so that you can track the size and versions. Also, you should be able to specify if you want the system files backed up, or just the user files. That would control the size and improve the backup and restore speed. Maybe Incremental for the OS, Differential for the User data.

ALSO - before you consider the ‘project’ complete, please try the restore process.
Nothing is more frustrating than having a working “WRITE-ONLY” backup system.

Please share your successes as well as your questions and failures here in the forum. You can teach us something.
(No I don’t work for them and I am not a volunteer, just a user)


Here’s a screenshot of 334GB differential backup from Comodo Backup:


There are 6 snapshots. If base is 111GB how is it that all differentials combined are 223GB if the size of my SSD is only 120GB with available 111GB? There is no way I would do so much writes to it, let alone have constantly new information as I use laptop for office purposes only.

I am backing up whole SSD on a partition level with free space too. I can’t choose what to backup as you suggested.

Can you explain this one? By write-only you mean I will only be able to create backup but not read it when restoring?
I don’t know if I have proper HDD around. If base size is 111GB that means target HDD must be at least of same capacity?


Let me see if I understand.
You have a 120GB drive in your computer. 111GB is available to your OS. You are making differential backups of “Disk-0”. First backup is a complete backup and takes 110GB, if I understand you correctly.
You have run a series of differential’s You now have a total of 334GB of data backed up.
As I have run differentials, they have all been inside the same backup (something.CBU) because I didn’t specify otherwise.
If files A, F, and G are modified right after the base is created.
If a differential is run at this point, only files A, F and G are backed up.
Now you modify files F and W and another differential is run, files A, F, G and W will be backed up.
When your Snapshot6 is run, it contains everything that was in Snapshot5 as well and the latest updates.
Remember that you are backing up your entire drive, so even OS files that are modified but are not needed are being included in the snapshots. (Think of the CACHE files, log files, the Temporary Internet Files, other temporaries and more).

When it comes time to restore, the base will be restored and the last snapshot. The previous snapshots are of no use when restoring a complete system. (That doesn’t mean that if file F was modified many times that you could not use the snapshots to get back to a previous version of the file)

I think that the numbers you present (111GB and 334GB) are reasonable, but possibly not optimal.

Remember that if you were doing incremental backups (not differential), that once the base is restored then each and every incremental backup would have to be restored in order before the next one or you would be missing data. Using the above example, the first incremental would contain A, F and G, the second incremental would contain only F and W, but not A and G.

Next, it is good to have a whole partition backed up, but why include the free space unless you plan to use UNDELETE someday after a restore.

My suggestion again is backup the whole drive and put that away for now. Using a different name, setup a differential or incremental backup for just your data (c:\Users\xxxx\ or even the whole C:\ drive). It lists the files that it is backing up, so look through that list (Did you know you can cut’n’paste the log from the GUI?). Exclude system files and temporaries to make it more efficient. I can do a differential of my machine in 15-20 minutes. A complete backup takes 1:45 to 2:00.

Finally, you understood exactly what I was saying. Good backups are only as good as the restore that can recover from a crash. Professional Disaster Recovery plans include going offsite and restoring your backups and seeing if your systems come back up. We should do similarly, Get a relatively inexpensive HDD and swap your SDD for it and see if you can restore your computer.
What happens if your computer were damaged and you could not get an exact replacement? Your bare-metal restore would not work because the processor, BIOS, peripherals and drivers would all be different. (By the way, when an SSD fails, it is dead. When a HDD fails, you can still get the data off of it in most cases)

For right now test your backup by trying to restore just one file that you updated a couple of days ago.

Today good backups cover mostly the data. You would get a new machine if your current one was damaged. You would have the current OS, then have to reload your application software (do you know where the license information and/or media is?). Finally, you would copy your data to the new machine and start putting the files in the right places to continue to do your work.

As one last thought, where are you keeping your backups? If you are like 98% of the population, your backup drive is right next to your computer right now. If your house were destroyed, what backups would you have available? Make a copy and put it in your detached garage or take it to your neighbor for “offsite storage”.


I had a few movie files when I did 2nd snapshot. Does that mean that even if I deleted them after snapshot 5, they were still included in snapshots 1, 2, 3 and 4 without software reflecting changes i.e. deleting movie files from each of 4 previous snapshots?

When restoring does software allow me to choose snapshot which I want to restore? If there are 6 snapshots can I choose 4th?

So differential would carry over previous snapshots while incremental would only carry changes between snapshots? Differential looks on base backup and current snapshot it does while incremental looks on difference between snapshots only?

Free space probably adds to data in each snapshot and if so, it’s for sure not optimal. I understand your point but I do partitional backups to be able to restore to new SSD or original laptop’s HDD and resume my work with least delays possible.

Does software allow to exclude temporary and system files like hibernation and pagefile or I need to specify filters manually?

I have external 2.5" HDD that I use for backing up. Do you suggest buying additional and checking whether I can restore backups from 1st external HDD and that this drive is able to work as bootable drive?

If this happens, I guess the only thing I can do is transfer data only if I did as you advice i.e. making selective differential and incremental backups?

On another HDD that you suggest to buy? Capacity must be at least of backup base size + approximate size of last differential or all incrementals?

This is the situation I hope won’t happen becayse I won’t be able to swap to new drive with restored data and resume work smoothly. Not sure what you meant by “(do you know where the license information and/or media is?)” did you refer to software apps on new machine? If you were speaking about removing bloated software from laptop then I did that once but I did not need license information. If you mean by re-installing Windows on new machine that has bloated software then I never did and if I would, I wouldn’t know where to find license information.

Yes I am in 98%. Today there’s online cloud backup solutions as well but with my upload bandwidth it would take months/years.

Deleting a movie after snapshot5 still leaves it on the previous base and snapshots, depending on when it was added/modified. It would still be recoverable as you suspected.

I don’t know enough about restoring a specific snapshot, but you should be able to go snatch a specific file and select which snapshot (version) you get.

Terminology: Yes, differentials write out anything that has changed since the base. Each snapshot in an incremental only has what was changed since the previous incremental. - When creating a base, the attribute that indicated that the file has been changed is cleared. Differentials do not reset this flag, so differentials continue to get larger. Incrementals reset the attribute so that unless the file is modified again, it will not appear on the next incremental.

Having the free space doesn’t make it easier to restore, it will take longer too. The only purpose of backing up free space is if you needed to use an UNDELETE function to try to recover a lost file. Have you ever used an UNDELETE?

At this point, I don’t think that CBU automatically skips any files. When I backed up my full system I did see a message that a few system files were in use and not available. They are not important - they are recreated as needed. I think you should start by looking at the list of files backed up and start excluding system and temporary files.

YES, get a “new” drive for your computer and practice the restore (bare-metal and new OS build).
To answer the next comment, practice getting your applications and data transferred to a different computer too. Then you will be familiar with what you will face if your computer dies and you can’t get an exact replacement.

No, the “new” hdd/ssd only needs to be as large (or larger) than what is in your machine now. 120GB if I remember correctly.

YES, you should be able to rebuild your OS and reload your applications. Someday it will happen.

just make a copy of your backup drive and take it somewhere outside of your house.


Thanks for your help Ernest

In terminology you described I think what separates differentials from incrementals is that former always use base as reference point and latter use previous incremental as reference point?

You know, I never used it and I assume it acts like recovery software restoring deleted files? When taking into account that I use SSD in my opinion backing up free space defeats the purpose of free space due to nature of SSD. The only reason I backed up free space is to ensure that backed up partition is 100% clone to original partition and with no reason I assumed this would increase the success rate of restore to new SSD in case something happens. I assumed that if something is 100% cloned to original then it’s integrity is 100% and there will be no errors when booting after restore from new SSD.

Do you know if Comodo Backup allows import of files or extensions I want to exclude from backup? Maybe I can find this list shared here in forum?

The problem is that I will then start Windows on another machine which will disable my license on current machine.

I have only heard about uninstalling bloated software but not with reinstalling Windows. I think reinstalling Windows will default to factory condition again with all bloatware included.

I will have to password protect backup then? I don’t think anyone would be interested to keep additional stuff which will only clutter their house. I will either have to use document locker rental and store there or bury somewhere like pirate buries his treasure…