In some situations, you may notice that certain Incremental backups are much larger than expected. This can cause issues for your Local backups and drastically increase the amount of Local Storage your backups are using.
Here's a list of several possible causes of unexpectedly large incrementals:
- SQL Database backups
- Image backups from other software (Windows backup, Macrium Reflect, Norton Ghost, etc.)
- Document management software can do weird things like zip and move files around which is seen as a change in data
- Log files being generated with the oldest entries being scrubbed or oldest files being removed, replaced, or renamed
- Disk Defragmentation on spinning disks
- Moving lots of data onto a drive that is already running an image backup
- Cryptolockers, if the data becomes encrypted the blocks have changed and we will need to back them up again
You should check if this has been happening before and establish a pattern to help determine the cause. For example, one case that we ran into was a larger incremental at the end of every week. It turns out, an end user was doing a Windows Desktop backup of their computer and saving it to the file server once a week.
WinDirStat or WizTree are two great applications for visualizing data usage. It could help identify what file(s) are behind the growth, if it's because of files or folders. It will lay out exactly how much space each folder on a system is using and probably point you towards the culprit.
If you can't (or can) find anything that jumps out at you, Beyond Compare or WinMerge are other great tools for comparing two files/folders. You can mount an image from before the growth, and then mount one of the massive images and it will be able to compare the two volumes and tell you what files have changed, but comparing full drives will take an extremely long time, so use it as a last resort.