Using Content Caching on a Mac

Whilst lurking in a Macrumors forum the other day, I came across a mention of something I'd just never heard of before - and it's really easy to setup.

If you have more than one Mac on your network, you can setup content caching, so that updates and iCloud downloads from Apple on one machine are cached for others on the network to use. Setting it up is just a few clicks, really simple.

Go into System Preferences, select Sharing, then click on Content Sharing and tick the box.


And - unless you run anything more complex than a single subnet on your network - that's it. Apple do recommend that you reboot any clients so they can take advantage of the cache. Full details are in this Apple support document, which also has links to other documents on more advanced settings (and how to set it up if you have a much larger network, for example).

Does it work?

I enabled my main Mac (a 2018 13-inch MacBook Pro - which is normally has a wired Ethernet connection, which is what Apple recommend). I then did an update to macOS Catalina 10.15.7 on my secondary machine (a 2020 MacBook Air, which is what I normally test any new updates on first).

You can see if it's working really easily using Activity Monitor (there's lots of detail in this Apple support article) - and for that update, Activity Monitor showed that 'Data Served to clients' was the same as 'Data Served from Origin': so not surprisingly, for the first update, the MacBook Air is pulling the update down from Apple, but it's doing that via the cache, and hence is populating the cache. A few days later, I updated the MacBook Pro - and whizz! - it went like a flash (because it's pulling the update straight off its own cache).

Activity monitor after the update shows that 'Data served from cache' is a bit more than that update.

Interestingly, the Last 7 days' 'Data Served' is quite large - I'd done some app updates on the MacBook Pro, and it's cached those, but these were after the secondary machine had already been updated, and before the cache had been enabled. I guess at some point (when the cache reaches the size limit I'd set for it), the oldest content will expire.

What about iOS devices?

You can connect an iOS device via USB to your Mac, and it will make use of the cache. I tried this by updating some apps on my iPhone (when connected to the Mac) and then doing the same with the iPad: however, Activity Monitor did not show that the cache had come into play at all. The implications of this Apple support article are that iOS updates will actually use the cache over WiFi - but I've not had an opportunity to try that yet. I will try some more testing over the next few weeks and post an update.

Is it worth it?

Well, it is extremely simple to setup, so if you have more than one Mac on a network, it's probably worth doing. I'd like to be more sure that it works for iOS devices to be able to pass judgement on that aspect, but if it does work, it might be worth doing - even via USB, which is obviously a hassle - if you have several devices and have a limited data allowance or especially slow Internet.

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