When browsing through iMazing backups using Windows' File Explorer and macOS' Finder, iMazing's backup folder appears to take up a lot of disk space, much more than the iTunes backup folder would for similar backups.
To put it simply, both the Finder and Windows' File Explorer are reporting the size wrong. The true size occupied by iMazing backups is, in fact, close to half of that reported size.
Why does this happen?
The short answer is because hard links are not accounted for by the Finder or Windows Explorer. Basically, many files end up getting counted twice. Interested in the technicalities? Keep reading. Otherwise, trust us: the size iMazing reports is the correct one.
The Long and Technical Explanation
In contrast to iTunes, which by default maintains a single backup of a device, iMazing keeps track of changes between backups. This makes your data much safer, protecting your backups against data loss caused by overwrites.
If you ever explore your iMazing backup location, you'll notice the following file structure:
Your backup location is comprised of a single folder for each device you are backing up. Each folder name refers to the UDID (Unique Device Identifier) of the device you are backing up. This folder contains the latest backup of each device.
You'll also find a subfolder named iMazing.Versions. This is where iMazing stores incremental snapshots of your backups, each snapshot containing only new and modified files.
Now, the first backup is entirely made of new files. So, it's the corresponding snapshot in the iMazing.Versions folder looks like an exact copy and is counted by the Finder and Windows Explorer's size evaluation routines as such. But this is incorrect - it is, in fact, a shallow copy which barely eats up any space at all.
The result of this miscalculation is that the first backup of each device you make in iMazing will appear to be twice as large as an equivalent iTunes backup. In fact, it is the same size, and even better, subsequent backups take up very little space. With iTunes, you would need to manually archive every backup version, which would, in turn, take huge amounts of space because iTunes does not track changes and will simply perform a new full backup after you archive the previous one.
"Shallow copy", how does that work?
Shallow copies are made possible thanks to a file system feature called hard links.
Hard links are directory entries that associate a name with a file on a file system. This means that it is possible to create a number of different names that all refer to the same data.
The advantage of using hard links, therefore, is the fact that virtually no extra space is being used on your computer.
There are a few things you can do to verify the true size of iMazing backups.
Open a terminal window and go to your backup location. Once there, type the following command:
Windows' command prompt doesn't handle hard links and will, therefore, also display inaccurate information.
The best way for getting a true representation of the folder size would be to install a third party Unix shell like MingW for Windows (http://www.mingw.org/) and run the same command as described above in the macOS section.