Are there multiple iPhones and iPads in your house? What about Macs, or Apple TVs? Have you ever thought about how much bandwidth all those individual Apple devices use downloading the same updates, media, and iCloud content as each other?
Content Caching is Apple’s solution to this. Mostly intended for large institutions, this feature allows a Mac to become a cache for every macOS, iOS, and Apple TV system on a network. Previously this feature was exclusive to macOS Server, but macOS High Sierra now offers it to all Mac users by default. This means caching is now free for home users to set up.
Setting up your cache is simple, and a good idea if you’re dealing with bandwidth caps, or just someone who wants downloads to run faster the second time around. All you need is a Mac running High Sierra, ideally one that’s consistently connected to your network via ethernet.
How to Enable Caching on Your Mac
First, choose a computer to serve as your cache. Ideally this should be a desktop Mac that’s connected to your network over ethernet—it’s possible to cache over Wi-Fi, but Apple doesn’t recommend it.
On that Mac head to System Preferences > Sharing.
On the Sharing screen check the “Content Caching” option in the left panel.
Just like that you’ve set up your cache. If you want to limit the size of the cache, click the “Options…” button at bottom right.
From here you can change where your cache is stored, and also limit how big it can get. To disable the cache later, simply uncheck “Content Caching.”
How Caching Works
So how does this actually work? Basically any software update, app download, iCloud document, or iTunes media downloaded on your network will end up in the cache. If another device needs the file it will check the cache first. That means it will grab it from that computer rather than the internet—making the download much faster and saving you internet bandwidth. To quote Apple’s explainer about content caching:
For example, when the first client on your network downloads a macOS update, the content cache keeps a copy of the update. When the next client on the network connects to the App Store to download the update, the update is copied from the content cache rather than from the App Store.
The cache is encrypted, meaning people with access to the computer hosting the cache cannot read the files directly. While somewhat annoying, this means users on your network don’t need to worry about you spying on their cached photos, which is probably for the best.
Multiple Caches For The Win
If you’ve got two Mac desktops in your house, you can become even more awesome by enabling multiple caches: just enable the cache on both devices. They’ll act as peers, as Apple explains:
When your network has more than one content cache, the content caches automatically become peers and can consult and share cached software.
Do you need to do this? No. Is it fast and super cool? Absolutely.
What Is (and Isn’t) Cached
You might be wondering what is and isn’t stored in this cache. Apple offers an official list; here’s our summary:
- Purchases from iTunes, both for Windows and macOS.
- iBooks Store content for macOS and iOS
- iCloud data, including documents and photos, to both macOS and iOS
- Garageband downloadable content
- macOS operating system updates
- Mac App Store downloads and purchases
- iOS applications
- iOS updates
- Various other mobile assets, including Siri’s voice and language dictionaries
- Apple TV updates
- Apple TV apps
- Purchases from the iBooks store
Note that, for legal reasons, some things may not be cached in certain countries. For example, iBooks purchases are not cached in Canada for legal reasons, and iTunes downloads aren’t cached in Brazil. It’s unfortunate, but Apple’s just trying to stay within the law.