iCloud Photo Library synchronization performance

Last Updated: Jun 24, 2021

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Up until macOS 10.12 Sierra iCloud Photo Library poorly managed available resources while synchronizing its database. More specifically, the Photos app would consume all available bandwidth, rendering your internet connection unusable. The result is a terrible synchronization performance.

Apple has considerably improved its iCloud Photo Library since it became available as part of OS X 10.10 Yosemite and iOS 8. As a former Aperture user, I did have some concerns that I managed to work through, and I found workarounds for issues like sharing libraries with family members. Nevertheless, iCloud Photo Library has a few remaining issues that won’t impact you on a daily basis, but when they do, they are a major pain in the butt.

Restoring an iCloud Photo Library from Backup

One of those issues is related to restoring an iCloud Photo Library from Backup.

Last weekend, I re-installed OS X 10.11 El Capitan on my iMac, hoping it would fix some of the bugs I had identified. Due to its size, I store my iCloud Photo Library on a LaCie 5big Thunderbolt 2 Raid. So re-installing OS X on my internal hard drive had no effect on my iCloud Photo Library. However, when I tried to open the library after the re-install was complete, Photos claimed that it had to delete incomplete items from my library and re-download them. The result was that Photos had to re-synchronize my complete library. That leads to a second and even more severe problem.

Synchronization Performance is Horrible

Synchronizing an iCloud Photo Library consumes all available bandwidth, making every other application that depends on your internet connection virtually unusable. My iCloud Photo Library is about 300GB large and synchronizing it takes a couple of days. I have a Comcast Business Class 150/20mbit internet connection, and Photos just kills it. Not even web browsing works properly while Photos is synchronizing. So I ended up pausing and resuming the synchronization process a lot. The problem is that not even at night we can afford to let Photos suck the life out of our internet connection because we use it to stream Netflix and other content via Apple TV.

iCloud Photo Library synchronization performance
Lifesaver: Pause for one day

Synchronizing an iOS device is not quite as bad because the amount of data transferred is usually less unless you choose to store original images on your device. I only have that setting enabled on my iMac, all other devices, including MacBook, iPhone, and iPad store device-optimized versions.

Apple Ought to Solve This Issue Soon

Most other cloud storage solutions manage available bandwidth and other resources appropriately. Just look at CrashPlan or Dropbox. So I can’t believe Apple hasn’t fixed this issue yet. The problem still persists as of OS X 10.11, but I hope it will be fixed in one of the next point releases. Until then, I avoid re-installing OS X or restoring my iCloud Photo Library from backup!


Besides all those issues, there is no viable alternative. iCloud Photo Library is nicely built into the Apple’s ecosystem, and it works well. Synchronizing new photos or edits of existing photos is a breeze. Paired with the fantastic camera of the iPhone 6 and 6S, it’s an unbeatable duo. 9to5mac recently had an excellent write-up about iCloud Photo Library, its issues and they compared how it stacked up to Google’s solution.

Fix available in macOS 10.12

Based on my experience with macOS 10.12 Sierra, I can report that the issue has been fixed. Photos now seem to sync without eating up all available bandwidth.

11 thoughts on “iCloud Photo Library synchronization performance”

  1. Hi Michael,

    I just installed the release of El Capitan and I’m exactly in the same situation as you …

    My library is located on my other internal drive so the fresh install should have no effect on my library. However, when I tried to open it, Photos told me that it has to delete incomplete items from my library and re-download them.

    So now, Photos tries to upload all my library to the cloud AND download it from the cloud …

    Did you find a solution ?


    PS : sorry for my english, i’m french ;)

    • Bonjour Sébastien! I didn’t find a solution other than restoring your old user account from a backup, which kind of defeats the purpose of a fresh install. I’ll try to find out more from the Apple Business team and will update this post with what I find out.


      • Hi,

        Thanks for your quick answer !!

        When you say “restore your old user account”, what exactly do you mean ? The entire user account ?? Is there not lot of problems doing this ?

        • Sébastien,

          you can restore your user account and settings from a Time Machine backup. But as I said, any corrupt settings or problems would get carried over, so I usually favor a clean install without restoring any user settings.


          • OK.

            Can you tell the size of your librairy and the time it took “re-sync” ?

            Pfffff . :-(

          • My library is about 330GB and it took several days. I had to pause and resume synching often however because the sync process killed all my available bandwidth. Apple really has to implement some bandwidth management…

          • Like the first sync …

            I was hoping never to do it again with my little bandwidth …

            Thanks again Michael

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