Differential backup is large

As a test, I created a disk backup, changed one or two files and then performed a differential backup. This was much bigger than I had expected. the original backup image is about 55GB and the differential 16.5GB.

Is this normal/expected behaviour?

Also, the user documentation seems to imply that I can make an incremental file backup based on a disk/partition archive. (See "Creating an Increment to a Full Partition Backup" in "Backup Scenarios"). However, the software won't let me. Can you do this? (I wouldn't surprised if not.)

Thanks,
Mike

 

Hello Mike456,

I did some testing on a 10GB partition with 5 GB of data. Ran complete backup of the partition, introduced 1.5GB worth of new data, and performed a differential backup. The differential turns out to be exactly also 1.5GB.

Did you perform any defrag prior to the differential backup? Also check in your advanced settings to skip OS auxiliary files and archive files.

How much new data did you introduced? What is the original size of the full backup hard drive compared to the 55 GB archive?

Is it possible that your original backup was compressed but your differential was not?

-Tommy

 

Hi Tommy, thanks for your response.

My hard drive is 320GB (when unformatted). There are two partitions, 250GB and 50GB, both NTFS, and I am backing up the first one (250GB, system partition) to an external USB disk.

The space used is 95.3GB and the size of the partition backup is about 60GB.

The size of the differential backup is about 17GB.

I can't believe I changed more than a few MB of data between backups.

Windows Vista Ultimate performs an automatic disk de-fragmentation every week; there was one between the two backups. Shadow copies and restore points are turned on (Vista default settings).

I am using default settings in Paragon Drive backup - I didn't change any compression settings. The log indicates that the page file is being skipped.

Mike

 

Hello Mike,

I think the defrag process had something to do with it. I will try to confirm this. If you could, can you test running a differential backup, introduced data immediately, and run another differential backup before the defrag. I suspect you will get similiar results to mine.

Tommy

 

Hi Tommy,

Today I did what you suggested - ran a complete backup of about 80G of data in the 250GB partition, changed one file, and then ran a differential backup.

The original backup size was about 61GB and the differential was 3.3GB. Much better, but still bigger than I expected: the size of the file I changed was 15KB.

I can only think Windows is making lots of changes "behind the scenes".

Am I alone in this, or do other users get unexpectedly large differential backups?

Mike

 

Hello Mike,

Surprisingly, this is the first time I've heard someone mentioned this. I would imagine it's Windows restore point that's doing this. Another test would be to run the same scenario but with restore point turned off.

Good luck,

Tommy

 

Thanks for your responses, Tommy. I have now found how to add a "Complementary File Backup" to a partition image - this is much smaller than the differential backup (although it takes a long time to run).

Mike