This article originally appeared in TidBITS on 2015-05-20 at 6:22 p.m.
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How to Throttle iCloud Photo Library Uploads

by Adam C. Engst

In networking terms, “throttle” means to control the flow of data. But the more colloquial use of the word is also entirely appropriate when it comes to how Photos for Mac performs uploads to iCloud Photo Library. Apple’s new service for centralizing your photo library in iCloud has caused untold frustration with how it can monopolize your Internet connection, transferring photos to iCloud as fast as it can to the detriment of all other network traffic (see “iCloud Photo Library: The Missing FAQ [1],” 15 April 2015). This may not affect everyone, but it’s certainly widespread.

My Internet connection runs at 30 Mbps down and 5 Mbps up, and when I turned on iCloud Photo Library for the first time, Photos completely destroyed Internet performance for every device in the house: Web pages loaded slowly, Google Hangouts struggled, Netflix buffered repeatedly, Rdio stuttered, and even Dark Sky on the iPhone timed out getting climate data. I had to promise to pause syncing whenever Tristan needed to do homework (which is whenever he’s home, it seems), and it was clearly something that couldn’t run during our work days.

Happily, our old friend Will Mayall (Remember Emailer and LetterRip? That’s Will.) came up with a solution [2] that at least some people will be able to avail themselves of. Given how long it will take to upload a decent-sized photo library, you could be doing that every morning and night for days or weeks. (And no, I have no idea what Photos thinks is happening when it says “Adding X items” after you click Resume; it goes back to uploading shortly thereafter.)

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Will’s solution revolves around Network Link Conditioner, a preference pane Apple provides to developers to test their apps under simulated poor network conditions. An iPhone app, for instance, has to work properly even if the cellular data connection provides only a few hundred Kbps.

To get Network Link Conditioner, you need a free Apple Developer account [4]. Assuming you have that, the next step is to download the Hardware IO Tools for Xcode [5]; you likely want the most recent release. After downloading, open the Hardware IO Tools disk image and double-click Network Link Conditioner.prefPane to install it in System Preferences.

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If you don’t have or want an Apple Developer account, TidBITS reader David Schaefer alerted me to the fact that you can download the free Onyx [8] utility and install Network Link Conditioner from the Parameters > Misc tab.

Once the Network Link Conditioner preference pane is open, click Manage Profiles, click the + button to create a new profile, and give it a name. For Downlink Bandwidth, Will recommends setting the limit to something near your connection’s maximum throughput; for Uplink Bandwidth, he found that 70 percent of your upload throughput worked well. Feel free to experiment with other numbers; you want them as high as possible without letting Photos impact the performance of other network apps. In this case, I’ve set my Downlink to 20 Mbps (leaving 10 Mbps of overhead) and Uplink to 3500 Kbps (you can’t use fractional numbers like 3.5 Mbps; that’s 70 percent of my 5 Mbps uplink bandwidth). Don’t change any other settings, since they simulate errors.

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Click OK, and if necessary, choose your profile from the Profile pop-up menu. As long as the switch in the Network Link Conditioner preference pane is On, your Mac’s bandwidth — and thus what Photos can do to your Internet connection in general — will be throttled. When it’s enabled, Network Link Conditioner puts an icon in your menu bar; you can deactivate throttling from that menu as well. Finally, Network Link Conditioner turns itself off automatically when you restart your Mac, so make sure to enable it again if you have to restart before your Photos sync is done.

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Once Photos finishes uploading to iCloud Photo Library, you should turn off Network Link Conditioner. But I recommend leaving it installed, because if you import a lot of new shots into Photos, it very well may take over your Internet connection again, necessitating a return to the Network Link Conditioner preference pane to rein in that unruly upload. Better yet, we can hope Apple will update Photos to be friendlier; apps like Dropbox and CrashPlan upload constantly in the background on all my Macs with no noticeable impact on overall performance.