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Vladimir Chemeris
Vladimir Chemeris

Posted on Originally published at storageradar.app AI-assisted

Inside a 9.8 GB Xcode Simulator: Apps Took 350 MB

#xcode #ios #macos #devtools

I build StorageRadar, a disk space app for macOS. Everything below uses built-in commands, so you can repeat it without the app.

Last week I measured where 51 GB of simulator storage went on my Mac. One QA simulator held half of the Devices folder, and a reader asked what was inside it. Short answer: not my app.

One simulator, 9.8 GB

The QA simulator is an iPhone 18 Pro on iOS 27.0. I measured it on 26 October 2026 while it was booted:

du -k -d 4 ~/Library/Developer/CoreSimulator/Devices/<UDID>/data | sort -rn | head -20
Enter fullscreen mode Exit fullscreen mode

Bar chart of the QA simulator's 9.81 GB data folder. Containers with all apps take 0.34 GB, the smallest bar.

Folder inside data Size
Library/Application Support/PRBPosterExtensionDataStore 2.88 GB
var/db/diagnostics 2.07 GB
private/var/MobileAsset 2.03 GB
Library/Caches/com.apple.coresymbolicationd 1.13 GB
var/db/uuidtext 0.49 GB
Containers, all app containers 0.34 GB

Everything my app and its tests wrote fits in Containers: 0.34 GB of 9.81.

Ten simulators side by side

I have 53 simulators. Forty-three hold about 20 MB each, the size of a device that never ran an app. The other ten:

Stacked bar chart of ten simulators' data folders, 0.63 to 9.81 GB. App containers take 0.07 to 0.34 GB on each.

  • App containers stayed between 0.07 and 0.34 GB on every device.
  • MobileAsset showed up everywhere, from 0.17 to 2.03 GB.
  • The poster store was big only on the two booted iOS 27.0 devices: 2.88 and 1.65 GB. On iOS 18.6 and 26.5 it stayed under 0.05 GB. Two devices prove nothing about iOS 27.0, but the gap is wide.

What the folders are

PRBPosterExtensionDataStore. The name, along with GalleryCache and SnapshotCache.cachedb, is a string in the private PosterBoard.framework of the iOS 27.0 runtime. Its subfolders carry the IDs of Apple's poster extensions: WeatherPoster, EmojiPoster, PhotosPosterProvider and others. Weather and photos are among the Lock Screen wallpapers Apple lists. On my QA device, 2,911 .atx snapshot files of about 1 MB each made up 2.9 GB. Apple doesn't document the folder, and I don't know what makes it grow.

var/db/diagnostics and var/db/uuidtext. The simulator's own copy of the unified log. man log describes a log store as a database like the one in /var/db/diagnostics, with uuidtext next to it.

private/var/MobileAsset. Asset sets the simulator downloads itself. On the QA device the biggest were named after Siri Understanding (805 MB), linguistic data (409 MB) and Siri text-to-speech (289 MB). Someone on the Apple forums reported this folder growing by tens of gigabytes on iOS 26.5. No answer there yet.

com.apple.coresymbolicationd. man coresymbolicationd calls it a "daemon to manage debug symbols cache". 1.13 GB on the QA device, close to zero elsewhere.

What I do about it

I don't delete files inside these folders. None of them is documented, so I can't predict what a half-deleted log store or poster store does to a simulator. I work on whole devices:

  • xcrun simctl erase <UDID> wipes contents and settings and keeps the device.
  • xcrun simctl delete <UDID> removes the device.
  • xcrun simctl delete unavailable removes devices the current Xcode SDK no longer supports.

An erase drops your installed apps and logins along with the system data, and the caches can come back once the device runs again. It buys space; it doesn't stop the growth.

The full version with every number, the measurement method and an FAQ is on my blog.

StorageRadar's Disk Map drills into folders like these, and its Dev Cleanup lists CoreSimulator under Review before cleaning, next to DerivedData and package caches: storageradar.app.

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