Can I enable iCloud Photos synchronisation simultaneously on iPhone and iPad?

Mitochondrion wrote:

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Could you please tell me what formats are no longer supported on the newer system versions?

Apple deprecated many media formats when macOS 10.15 Catalina came out, when macOS went 64 bit only. At this time they removed some old iLife frameworks from the system, a final nail in the coffin of Aperture and iPhoto. The problematic legacy codecs have been described for iMovie in the document About legacy media in iMovie for macOS - Apple Support, but the document has been pulled by Apple, because it is old and the link is now broken.

You can still find a copy in the Internet archive, at

https://web.archive.org/web/20190328091358/https://support.apple.com/en-us/HT209029

It may take a while for the page to load.

For myself, to be on the safe side, I have converted all files that are not RAW to either HEIC or JPEG, and converted all videos to HEVC or H.264.

You may want to check primarily very old videos and recently imported photos, that have been shred with you. Image files, that are essentially links to the web with filename extension .webpage can make the cloud syncing hang, also pdf files.

Turning on iCloud syncing will work for everything at once-- turn them both on! Just to be clear, iCloud Photos is a synchronization service. When you engage iCloud Photos on a device, then the Library on that device is kept just the same as the iCloud Photos Library. So, for instance, if you take a picture with your iPhone, it is added to the iPhone's Photos Library, copied to iCloud Photos Library, and then copied to the Photos Library on each of the other devices that you have connected. If you delete a picture on your Mac, then that picture is deleted at iCloud and on all the other devices. 

So, the whole point of iCloud Photos is to have it connected to multiple devices. You do need to be sure you have room on both your devices and at iCloud.com. The free 5GB, for instance, would be good for only a few hundred pictures.

iCloud Backup is entirely separate and, if iCloud Photos is turned on, then Photos is not included in the backup--that would be doubling the storage.

iCloud Photos syncing is a sort of backup, but only partly. If your Mac gets run over by a truck, then your pictures will still be available through iCloud Photos. But if you accidentally delete the pictures of your sister's wedding, don't expect to go to iCloud and get them back-- they were erased there, too. iCloud Drive is a synchronization service, not an offline storage or backup service. If you don't have a Mac, then the best practice is to periodically copy everything to a hard drive for a real backup.

You're right-- when you delete pictures from your Photos Library, as a safety they can still be found in the "Recently Deleted" view for 30 days, and Recently Deleted can also be accessed from any connected device. However, if you were to scan through the posts here, you would see that an amazing number say, paradoxically, "How can I recover my permanently deleted pictures." Many people defeat the safety feature by deleting pictures from Recently Deleted, and then regret it. So-- the warning. Also, some disasters occur after 30 days.

Also, Photos is a non-destructive editor, so even if you do some crazy edit that you find embarrassing later, you can always revert to the original. As long as you have it.

Another thing: You can use "Optimize Storage" on the Mac, on your iPhone, or on your iPad. If you set a device to "Optimize Storage," then Photos may store only smaller images on the device and rely on iCloud to keep the full sized images. So, if Optimize is chosen, and you want to magnify a picture to see more detail, Photos will reach out to iCloud to get a full sized image for you to zoom in on. It's the same for editing or printing or anything that demands the full picture. Your optimized Library may take up less than 20% of the space of a fully downloaded Library.

I use "Optimize Storage" on my phone, but never on my Mac. If you "Optimize" on the Mac, then backups will only preserve the smaller images and not the originals.

I use Time Machine to back up my Mac. Time Machine does an incremental backup every hour if it's plugged in.

It copies only things that have changed so it uses very little space each time. I use a MacBook, so I only plug in the Time Machine drive at night. But if I suddenly discover that I erased a picture or file I want from last December, I can go into Time Machine and recover it. Or December 2023.

And, as you say, monthly (or so) I drag the entire Photos Library to a separate external drive as an additional backup.

Well, that's a lot! I hope it helps…

Mitochondrion wrote: … What happens if I decide to disable iCloud Photos, disable "Sync this iPhone/iPad"? Will the photos remain on the device or completely deleted? If the photos remain, will they be in the original high-resolution format?

If you're not using "Optimize," and you turn off iCloud, then the full Library will continue on your Mac and other devices with all your originals, just fine. (Still, backups are good!) The Library will remain at iCloud.com for 30 days, if you change your mind.

However, if you have "Optimize" selected, then things are more problematic. The "orphaned" preview pictures will be deleted from all your Libraries, since they aren't fully there, anyway. Again, your iCloud.com Library will remain for 30 days in case you change your mind, and you can download pictures from there. But then they won't be part of your Library, so you'd have to download both Originals and Edited versions, and they wouldn't be connected together like they were in your Library.

If instead of Optimize you use "Download Originals" on your Mac, but you do use "Optimize" on the other devices, then the Mac's Library will remain compete, but the other devices wouldn't have space for the originals, and so their "orphans" would be removed.

If you have Optimize on your Mac, and you later decide to change to "Download Originals," it will always be hard to tell if all the Originals have been re-downloaded. You have to check every picture, I think.

If you don't have "Optimize" chosen, then turning off iCloud is really simple. It's one of the many reasons I don't use "Optimize" on my Mac.

Mitochondrion wrote:

I have an iPhone running iOS 18.3.1 and an iPad Pro running iPadOS 18.3.1. I also have iCloud+ subscription. ...

Should I enable "Sync this iPhone" setting first and let it completely synchronise and then once it has done that then do the same on the iPad Pro? Or is it completely safe to enable it on both device and not worry about conflicts or any other possible issues?

[Re-Titled by Moderator]

It is o.k., as long as all devices are having the same and the most recent system version. The sequence for enabling the iCloud syncing may matter, if the system versions are very different. If the system versions are very different, it is safer to sync first the devices with the oldest versions with iCloud and later the devices with the more recent system versions. The problem is, that some image and video formats used on the older devices may no longer be supported on the more newer system versions, and it will be easier to handle them first, before trying to sync the newer devices. iCloud Photos will also have to handle adjustments, that are no longer available, or Filters, that have changed. This will be seamless, when upgrading to new from old to new and syncing the older devices first.

Mitochondrion wrote: …What happens if my Mac Photos Library size is 400 GB and my iPhone has 126 GB storage,

If you don't have "Optimize" checked, bad things. One of the things that produce problems that we see here is full storage spaces. There needs to be enough free storage space for the devices to be able to move files around.

For "Optimize," here's an example. My Photos Library has only "Favorites," and on my Mac it is 134 GB. On my Optimized iPhone, it's 4.5 GB. That's pretty remarkable.

what will happen if enable iCloud Photos on the iPhone, either from a brand new iPhone from upgrading or enabling Sync this iPhone setting after some time on a current iPhone from disabling Sync this iPhone setting?

If on a phone you turn off iCloud; then you make changes on the phone and/or at iCloud; and then turn you iCloud back on-- pictures will fly back and forth between iCloud and the phone, adding but not subtracting, until the Libraries are the same, again. Pictures in one place aren't deleted just because they are absent from the other place. Photos will try to avoid duplicates.

The biggest hassle with formats is videos-- ".mov" doesn't always mean the same thing, for instance. It's hard to tell.

Mitochondrion wrote: … But my mother has an iPhone and iPad combination. No Mac.… iCloud Photos enabled on both devices with Optimised Storage setting. What do I do for her? She does not need a Mac

That sounds fine. There's no simple backup, but you could download the images from iCloud.com to a computer for her every once in a while, just to get a backup.

You could even add a User to your Mac, sign in to her Apple account once a month or so, and download to an external drive for her backup.

Mitochondrion wrote:

So, iCloud.com Photos Library is the master library and the Mac System Photos Library is an offline version of the iCloud.com Photos Library.

Yes. When you are using iCloud Photos, iCloud Photos contains the master library, and the Photos libraries on all of the devices synchronized to iCloud (whether iPhones, iPads, or Macs) are local cached versions of that master library.

They might, at times, contain stuff that isn't in the master library yet. If your iPhone is far from any Wi-Fi hot spot and you take a bunch of pictures, it might wait until you're reconnected to Wi-Fi Internet service (and power?) to start uploading them to iCloud. But each device will try to synchronize against the master library, in iCloud, when it can; and in this way, the devices will indirectly synchronize with each other.

Mitochondrion wrote: So, iCloud.com Photos Library is the master library and the Mac System Photos Library is an offline version of the iCloud.com Photos Library.

The iCloud Library might be thought of as "master" only in two ways-- it is central (iPad and iPhone don't connect to each other, but everyone connects to iCloud,) and iCloud has the Originals, while other devices may have only previews. But that second thing is a choice.

My Mac has the Originals so, except for it not being the center, it is every bit as "master" as iCloud. iCloud simply copies whatever I do on my Mac. Other than "centerness," the 'Master" thing may not be a helpful concept.

Mitochondrion wrote:

What happens if I decide to disable iCloud Photos, disable "Sync this iPhone/iPad"? Will the photos remain on the device or completely deleted? If the photos remain, will they be in the original high-resolution format?

How to turn off iCloud Photos - Apple Support