Mark Gutz writes in with concern about a dialog that appeared in iOS (see figure):
I’m trying to sync my devices to use photos in iCloud, and when I try to turn on iCloud Photo Library on my iPhone, I get this message!
This is an absolutely frightening thing to be presented with, especially as in Mark’s case, iOS warns him that it will be deleting over 15,000 items.
The issue is that iTunes-based media syncing and iCloud Photo Library syncing cannot be active at the same time. If you’re old school, and have iTunes handle importing images from your iOS devices and syncing back albums and other collections, you have to give up this entirely when you switch from iTunes to iCloud Photo Library. However, it won’t delete any media from your Photos library in OS X. Apple says the reason for this is that iTunes downsamples synced images in an incompatible way.
Instead, it will delete all the iTunes synced data from iOS before then downloading optimized or full-resolution images and videos to your iOS device. (In most cases, you’ll use optimized images, because unless your photo library is relatively small and you have a 64 GB or 128 GB iOS device, you won’t have enough storage on most iOS devices to retain the full versions.)
Because this media has been synced to the iOS device, that means 100% of it is resident in OS X in your Photos library. Therefore, you won’t lose any media when you tap Remove Photos and Videos. To be sure, I always recommend a good backup. Make sure through visual inspection that all your media on the iPhone is in OS X, and that you have a backup of your Photos library in OS X.
Also, while iTunes can sync media in Photos that’s referenced in the library without being imported, iCloud Photo Library only sync files stored within the main Photos library. (There’s an option in Photos > Preferences lets you choose between copying media or referencing it.)
Once you’re sure everything is copacetic, tap the Remove Photos and Videos link, and iOS will churn away deleting all the iTunes synced items and begin what can be a very long process of downloading thumbnails or full-resolution images.
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