iCloud Photos "Optimize iPhone Storage"

[Mcrumors David]

Checked "Optimize iPhone Storage"...

->>> How long are originals (when downloaded) kept on the iPhone?

(Full-res Photos / Videos are downloaded when I click on them ...when is the cache cleared?)

 

[contacos]

It depends on how much space you have left on your iPhone and as far as I know it also takes longer to offload certain photos if it learns that you are more interested in those than others. For example I have an iPhone 11 with 64 GB of storage, right now I have 10 Gb "offline" on this iPhone while I have over 40 GB "offline" on my 128 GB iPhone 12 PM. In fact, on my old XS Max (64 Gb - 20 GB remaining) it stored only about 5 GB "offline"

 

[Mcrumors David]

I wonder if I can turn off iCloud Photos and then force the phone to "re-learn" / delete all cache !?

 

[ApfelKuchen]

There is no hard-and-fast answer, because removal becomes more aggressive as available storage space on the iPhone drops - the less available storage there is, the more aggressive the removal will be.

You might say the "cache is cleared", but to me that term is more appropriate for temporary caching (buffering for active upload/download, undelete/crash recovery, etc.) - to me "clearing" deletes the entire contents of the cache (like the caches that are deleted during a Mac's Safe Boot) - that doesn't happen with iCloud Photos; library contents are managed on an item-by-item basis.

To give you one person's example of Optimize Storage behavior - my 64 GB iPhone has 18 GB Available storage. 3.6 GB is utilized by Photos (which includes the full library of thumbnail images along with whatever full-quality images are currently on-device). However, I have 104 GB of images up in the cloud. (My 128 GB iPad is using just 2.8 GB for on-device Photos storage, yet it has 70 GB of Available storage.)

There's a substantial number of other iOS and Mac apps that behave in ways similar to Optimize Storage. The Music app is a prime example. Not only can you choose whether to permanently download songs vs. stream them, but there's an Optimize Storage option at Settings > Music where you can choose the size of the on-device library. Settings > App Store > Offload Unused Apps. iCloud Drive and Notes manage things automatically, with no options. If you use Messages in iCloud the on-device storage will also be automatically managed (individual messages removed from the device if they go un-read for an extended time, re-downloaded if/when accessed again). IMAP mail accounts are similarly managed - headers will remain on-device, message text re-downloaded as required.

And there are probably plenty of other examples, including third-party apps - on-device storage can be very limited, user data just keeps growing and growing.

 

[ApfelKuchen]

I wonder if I can turn off iCloud Photos and then force the phone to "re-learn" / delete all cache !?

I'm not sure why you'd need to force iCloud Photos to "relearn" - essentially each image stores a last-viewed date, and that date is used to determine priority for removal. It's very similar to the way RAM is managed on Mac - data/code remains RAM-resident based on a combination of its last-accessed date/time and the system's need to move new data/code into RAM.

If you turn off iCloud Photos you'll encounter several options: "Remove from iPhone," "Download Photos & Videos," and (fortunately) "Cancel." So yes, you could do this to "delete all cache." Assuming you were to "Remove from iPhone" and then activate iCloud Photos again, you'll end up re-downloading the full library of thumbnails and few, if any, full-quality images. In my experience the full-quality images won't download until you try to view them (basically, this is the same thing that happens after someone erases and restores a device, or sets up a new one).

It could be a way to minimize the size of the on-device library, but because iCloud upload/download activity requires separate storage space for temporary caching (it's part of the "Other" in Settings > General > iPhone Storage) I've seen situations where the library gets stuck in limbo - nothing uploading or downloading due to an absence of available device storage for the temporary cache.

My feeling is, unless it's clear that something is clearly malfunctioning trust Optimize Storage to manage the on-device "cache." As you saw in my previous post, my on-device storage is about 3-4% of the size of the cloud-based library, and it's likely half of that 3-4% is thumbnails, so maybe I'd recover 1-2 GB by doing the whole "Remove from iPhone" thing, and that savings would evaporate as soon as I started viewing old images and taking new images. Doesn't seem worth it.