The size of incremental backups often surprises people.
All you do is edit one small document, and the next day your incremental backup ends up being gigabytes in size – that doesn’t make sense, right?
But it does make sense, because Windows is a very busy operating system.
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Your data versus “the system”
We tend to think in terms of our own data: the documents we edit, the pictures we upload, or the work we do on our computer.
And, indeed, backing that data up daily is a critical part of what it means to back up at all – these are all files we don’t want to lose in case of failure, and files we expect our backup regime to take care of for us.
But it’s easy to overlook the fact that there’s a lot more going on than what you and I do.
There’s the operating system itself.
And it does a lot.
Windows changes a lot of files
Even if you do nothing with your computer for an entire day – nothing at all, it’s running but you never touch it – Windows is still hard at work.
Programs that make up the operating system itself are running. Programs that autostart when you log in are running. Updates are being checked, both by Windows and other software programs.
Your security software is running and scanning periodically, as well as checking for database updates and more.
There’s just a lot going on – and all that “going on” means that files are being changed. Files like:
- The system swap/paging file
- Temporary files
- Data files used by individual programs (like your security software)
- The Windows registry – its database of configuration and other settings
- The Event Log and other logging files
All that is in addition to whatever it is you’ve used your computer for, and often represents much more of a day-to-day change than you may have directly caused yourself.
Your programs change more than you think
Additional culprits include the software you run. They often change much more than just the files you work on, and some change files even if you didn’t actually “work on” anything at all.
If you fire up, say, a word processing program, you would expect that your document would change, of course. But in addition, that program may also cause changes in:
- Its own administrative files, which keep track of things like most recent edits, undo information, or documents recently accessed
- Temporary files used as part of doing its work
- Settings or other information may be updated in the registry
- The system swap file might be updated
Even for programs where you, yourself, don’t “change” anything, things change.
For example, if you browse the web, everything you view has been downloaded to your machine and placed in your browser’s cache. This cache then appears as a “changed” file, and would be included in the next incremental backup.
Even though you didn’t change anything, the programs you use change a lot.
Controlling backup size
With so much possibly changing every day, it’s important to realize that this is how your computer works, and you really do want to back all that up. When something goes wrong and you want to restore to a backup taken on a particular day, the changed information might well be critical to getting your system back to the state it was in when the backup was taken.
But, aside from getting a larger external disk for backups, what else can you do to manage the size of your backups?
Choices fall into two buckets: backup less data, or back up less often.
One thing I strongly recommend doing is running Windows Disk Cleanup. It will allow you to remove a number of things you may not need and that contribute to the size of your backups. Similarly, CCleaner, while overlapping some with Windows Disk Cleanup, will also clean out more things, particularly for many applications that aren’t part of Windows itself.
Many of the things that Windows Disk Cleanup and CCleaner remove may come back as you use your computer, but much of it will not. For all that doesn’t come back, your backups – particularly the initial full image – will be smaller.
While not my first choice, you can also alter how often you take incremental images. If you take them every day, you might schedule them every other day instead.
What to expect
Unfortunately, I can’t really give you hard numbers, or even percentages, of what to expect in terms of size for your own incremental backups. It varies, due not only on the backup software you use, but also exactly how you use your machine and what software is installed and running on it. One person’s incremental backup might be one tenth the size of another’s, and it could all be quite appropriate and necessary.
What I can say is that I’d much rather have you back up too much than not enough. . . and that means the easiest solution might well be that larger external hard disk I mentioned earlier.