"iPhone Storage Full."

It's a dreaded notification that some iPhone users have come to experience. It happened to me at my most recent holiday gathering while taking family photos. It wasn't the first time, but it was certainly an inconvenient time.

Like most people who receive the storage full prompt, I immediately went to Settings, followed by General, then the iPhone Storage option in order to see what was taking up 256GB of space. Sure, I snap a lot of photos and there are dozens of apps on my phone that I no longer use that could be taking up much needed storage space. I hoped that if I found what was taking up so much space, I might be able to delete it and clear up some storage**.**

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But, no. It wasn't photos, or apps, or files, or documents that were filling up my iPhone this time. It was "System Data." Eighty whole gigs of my iPhone, roughly one-third of its entire 256GB of storage, were being taken up by "System Data."

System Data on the author's iPhone ballooned to 80GB on Thanksgiving. Credit: Mashable screenshot

When I looked online, I found posts and threads on social media where other iPhone users shared their own System Data storage issues. One Reddit user had their System Data taking up as much as 128GB of their 256GB iPhone!

And worst of all, there's nothing we could do about it.

What is System Data?

When clicking on System Data, the very last thing on the iPhone Storage settings page where all your apps and their file sizes are listed, iOS provides a very general explanation of what System Data is.

"System Data includes caches, logs and other resources currently in use by the system," it reads. "This value will fluctuate according to system needs."

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Here's how the iPhone describes "System Data." Credit: Mashable screenshot

To be clear, this isn't the drive space that the operating system needs. That's listed completely independently under iPhone storage. The same with data connected to each individual app. That's rolled into the size of each app. This is some vague other thing. I reached out to Apple for more information. 

"System Data encompasses caches, logs, and other resources currently in use by the system," Apple said. "This also includes temporary files that have a short lifecycle and are actively being used by iOS to keep the iPhone running smoothly."

You'll find that System Data fluctuates wildly. That 80GB of System Data on my iPhone that I mentioned earlier? It was down to 50GB the next morning.

"The size of System Data is managed by the system," Apple said. "When the temporary files are no longer needed, the system cleans them up automatically, so changes to the size of System Data are expected."

How can users clear iPhone's System Data?

According to Apple, System Data is basically what iOS decides it needs to store pertaining to apps and other processes that are currently running or being used. But, what if a user wants to remove those temporary files immediately to open up space. Is there anything a user can do?

"iOS is designed to monitor and optimize storage usage, removing as many temporary files and caches as possible to free up space as needed without any required action from the user," Apple said. "This automatic management takes into consideration the amount of available storage and helps ensure iPhone maintains optimal performance while preserving storage space. There isn’t a need for users to do this manually."

So, in short, no. There's nothing iPhone users can manually do to clear up unnecessary System Data when storage space is needed. iOS decides when and what to clean up. One Redditor on the previously mentioned Reddit thread even shared how their iPhone's 167GB of System Data suddenly dropped down to 4GB on its own.

However, based on what Apple says and my own experience, this is what I'd recommend:

As soon as you notice your System Data is getting out of control, close all your unused apps out completely. To do this, simply swipe starting from the bottom of the screen and go upwards. All of your open app windows should appear stacked one behind the other. Swipe those windows up to completely close out the app. The System Data won't clear up immediately. Again, Apple says users can't control this. However, closing those apps did appear to move the process along as those temporary files are no longer needed once the apps are closed.

Hopefully, one day, Apple will allow users to force iOS to clear up System Data. But, until then, this is the best iPhone users can do.