How does Backupper detect file changes in Image backup
I am trying to figure out a way to backup a Veracrypt data. When I backup a Veracrypt partition, I notice that backupper is unable to integrate with Veracrypt and do a sector by sector partition. This is not desirable size-wise, a 5Tb partition that is mostly empty will result in a backup that is 5TB in size.
Instead of using a encrypted partition, I leave the partition as exfat and then create a giant veracrypt file container. What we end up with is a 5 Tb veracrypt file. I then proceed to image backup the volume. What I have notice is that while the backup is really slow (it has to process 5 TB of data, so it's going to take like 24 hours), the resulting backup only contains actual used data. A 5 Tb container with 200 Mb of files will result in a 200 mb backup. If you add another file, and run increment or differential backup, only what was changed will be backup (but still takes like 24 hours even if the file is only 1K). I have tried restoring and it appears to work so far.
My question is how does this work? How does backupper notice the change in the veracrypt file? What could cause the backup to break?
Thanks.
Comments
Generally, for the encrypted drive, AOMEI Backupper will use a sector-by-sector backup way by default. That's to say, it will back up all sectors, whether used or not.
When you create the veracrypt file container, the properties of the volume is not encrypted (only files in the volume are encrypted), AOMEI Backupper will only back up used sectors.
AOMEI Backupper actually will detect the change of sectors, not file changes.
For encrypted drive, AOMEI Backupper cannot parse the file system, so it takes a long time to back up the entire 5TB space sector by sector.
Did you create a partition backup for the virtual drive?
And, it seems that the veracrypt container file on the drive is incompressible. So, the backup file is approximately equal to the size of file.
Generally, it will compress your data to the backup image. The backup size is affected by the data amount of compressable, and the total size of backup data. For the empty sectors, the compress level will be high. For the 80gb file, if it is incompressible or the compressible level is low, so the size of backup file will be close to the size of data.
It seems that these files in veracrypt file container can't be compressed by our program.