84GB of cache files on my 256GB iPhone: Frustrating

The other day I started getting error messages about my iPhone being out of storage. This is unusual for me because I try to ensure everything is on the cloud. My philosophy is that my device should not be the centre of the Universe for me, in case it breaks or gets stolen. That's also one of the reasons I routinely purchase the 256GB iPhone version, rather than the 512GB or 1TB+ devices. It forces me to avoid keeping things local.

In practice I will usually use about 100Gb on apps and then stuff another 50GB of unnecessary but useful data - movies, audiobooks, one or two super-size apps like Age of Empires Mobile (1.18GB!) and so on. Plus I'll let the iPhone manage an on-device cache of photos and video.

So everything is usually well managed.

Until, that is, I got an 'out of storage' error message. Basic functionality stopped working.

I noticed that the iPhone was offloading as many apps as possible and this was beginning to impact my ability to get things done as I would – for example – find a random banking app unavailable because it had been offloaded to save space.

What was going on?

Simple. My device had about 84GB of 'system data' on it. Plus the 13GB of system files. So almost 100GB of my 256GB storage was spoken for.

I worked around it by removing some unnecessary media. But the 'System Data' stayed the same. Indeed, it slowly ticked up.

ChatGPT and Claude were sympathetic but not that helpful, essentially because Apple is a bit opaque when it comes to this 'System Data' folder. I offloaded, deleted and messed about with various apps in the hope that one of them was a key offender.

I followed the equivalent of some 'old wives tales' on Reddit with users insisting the issue was Discord, or Gmail, or some other app. It wasn't. I deleted and restarted those apps and felt like a bit of a muppet for believing them!

After a few loops around with my AI agents and some comprehensive Googling myself, I decided to simply reset the device and reinstall from the latest iCloud backup I'd made. I didn't want to do this: It felt a bit unnecessary.

Well, in 2025, it is ridiculously unnecessary.

But, I reasoned, I can't continue to mess about with an iPhone that only had 159GB of space accessible to me. (That's 84GB mysterious system data + 13GB system files)

I closed my eyes this morning and did the reset.

Within 10 minutes, it was all done. I checked and found 7GB and then 20GB of 'system data'. That's a bit more manageable. I'll need to monitor things and try and determine what might be causing it.

I was giving some strong thought to trying to look at error messages via Xcode (if I plugged in the device to my laptop) but I reasoned I didn't have time to be fiddling.

The one piece of advice I'd give you, if you're going to do this, is to make sure you're 'at home' or somewhere there's a bit of continuous WiFi.

I did the reset then had to head out to take one of the children to a sports game for the whole afternoon... before basics like WhatsApp and my password manager had downloaded!

Unfortunately, the iPhone won't let you use your data connection to do this restoration so I spent the afternoon in a bit of a haze until I got back home and into WiFi once again!

It's still at about 20GB of 'System Data' so I am content. I'm also pleased that I was able to retain the eSIMs during the reset and reinstall process - good work on that Apple.

If anyone from Apple is reading, could you a) fix it so that 'system data' is far less opaque to try and give users suffering from huge 'system data' collections a clue about what to delete/reinstall. Or simply fix it so that system data folders are kept in check.