iPhone 18 Pro system data file is large after restoring from backup

Found it!! It was the OneDrive app. Over 50Gb of data in the backup file. Deleted app, and it dumped it from the System Data file. System Data file now just a couple of Gb 🥳

Your post does not clearly specify whether the backup was performed via iCloud or iTunes/Finder.

When you back up an iPhone using iCloud or a computer through Finder or iTunes, system caches, temporary files, and other disposable system data are not backed up as ordinary user data. These files are generally recreated by iOS when needed rather than transferred to the new device as part of the backup.

An iPhone’s System Data storage category can include caches, logs, temporary files, downloaded resources, and other data used by iOS and apps. The amount of storage occupied by these files can fluctuate considerably depending on device usage, software updates, streaming activity, and other factors.

When you restore a backup to a new iPhone, supported settings, app data, and other information are transferred, while caches and temporary files may be discarded, rebuilt, or recreated as necessary. Consequently, the System Data storage reported on the new iPhone does not necessarily match the amount reported on the old one.

Therefore, claiming that 72 GB of System Data on the old iPhone was backed up and then restored in its entirety to the new iPhone is not technically justified. The fact that the new iPhone shows a large System Data figure does not prove that the same 72 GB of system files was transferred from the old device. The new device may have accumulated its own System Data after restoration, and the displayed storage categories can change over time.

If you want to verify this for yourself, take a fresh backup of your new iPhone and restore the device from that backup. Then check its System Data storage again. You will see why the amount of System Data is not necessarily preserved across a backup and restore. The precise result may vary, because iOS can rebuild caches and other temporary data after restoration.

The key distinction is that restoring an iPhone backup does not clone every file on the old device, including its caches and temporary system files. A storage figure of 72 GB, by itself, is not evidence that 72 GB of System Data was included in the backup and transferred to the new iPhone.

nigel106 wrote:

So, I created a backup from my new iPhone 18, wiped it, and reloaded it from iCloud. It's created a System Data file of over 70Gb again! Is this correct? Everything I've read suggests they should be no more than 20Gb. Any ideas, please??

What you read may have been about an older phone without AI. A new phone with AI could well have such a large System Data allocation. You just proved it, because what you did is the only way to minimise System Data.

Monitor it over the next week or so, it may optimise.

Many thanks for such a detailed response. I’ll try this over the weekend. Really appreciated 🙂

P.S. I just followed the instructions on the screen, but loaded the new phone from iCloud, not the old phone.

So, I created a backup from my new iPhone 18, wiped it, and reloaded it from iCloud. It's created a System Data file of over 70Gb again! Is this correct? Everything I've read suggests they should be no more than 20Gb. Any ideas, please??

nigel106 wrote:

Found it!! It was the OneDrive app. Over 50Gb of data in the backup file. Deleted app, and it dumped it from the System Data file. System Data file now just a couple of Gb 🥳

Wow, naughty Microsoft! That may explain a recent surge on mine! I also dumped One Drive recently.