Migrating existing Photos library on an external drive to new Mac with iCloud Photos - conflict?

I finally replaced my 2012 Mac mini which had it’s system Photos library stored on an external. iCloud enabled with originals downloaded. I disconnected that drive and attached to the new Mac which upgraded the old Photos library (old Mac mini running Catalina). But when I try turning on iCloud Photos I get a message that I may not have enough space in iCloud. Is there a trick to migrating in such a way that the Mac/iCloud recognize that all of these local photos are already all in iCloud?

how big is your photo library and how much free icloud space you have? I got a feeling (just gut feel, have not researched this) that icloud requires the free space of the same size as your local photo library to start working out the sync, etc.

may be Power Photos may help?

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I believe I used an app like Power Photos years ago. I’ll look at it but on first glance I’m not really sure that it would help.

According to iCloud my Photos library is around 102GB and I’ve got 70GB free. So not enough to cover it. I guess I was/am hoping that iCloud is smart enough to analyze my Photos and determine that what I have locally is the same content as in iCloud and that nothing actually needs to upload. I know I can start fresh and just re-download the images but… lol, really??? That as a lot of data to use and while my mobile hotspot is technically “unlimited” I’d like to avoid any issues if possible.

Mostly I just need iCloud and the Mac to talk and compare notes and then agree that everything is good.

I think iCloud need some staging area (storage space) to work. Perhaps others from this forum can offer some help

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Apple offers a “free personal session with a specialist” when you set up a new Mac for set-up so I figured I’d give that a go! I’ll report back if I get a resolution that might be helpful to others - scheduled for tomorrow morning.

excellent, great thinking. Might as well use their “genius” to help

You could upgrade your iCloud storage, make the conversion, then downgrade to your previous storage level. Will cost your a couple of bucks for the extra storage for a month.

Yeah, I may end up doing that. I guess what I was hoping to confirm was that it won’t start re-downloading or uploading the photos that are already in both places. Is iCloud/Photos smart enough to look at images in each place and know they are the same? I would assume so but, lol, well, maybe not!

This is counterintuitive, but you might actually want to download the photos from iCloud rather than trying to sync the local library. Bear with me a minute here …

When an iCloud connection is interrupted in any way (sign out of iCloud, modify the photoslibrary system file) on a Mac with a large Photos Library in which photos are stored in full resolution, Photos must check each picture file (one at a time) with the picture files in iCloud. Depending on the size of the library and your internet connection, this could take weeks.

I don’t know for sure, but this one-by-one check may be thing that requires the extra iCloud storage. Or maybe iCloud must reserve enough storage space to accommodate your existing iCloud Photos library plus the local Photos library content, in case the local photos all need to be uploaded to iCloud.

It turns out that it is much faster to avoid that one-by-one check and just force Photos app to download all photos from iCloud. As stated above this is counterintuitive. This is explained completely in the Alison Sheridan’s Podfeet blog:

Read the blog post carefully to determine if your situation is appropriate for the proposed solution.

Hope this helps!

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Thanks. I have a new podcast and her post is helpful. It matches my experience in the past with iCloud Photo Library and checking images.

A very weird thing happened this morning… I had the thought that maybe I would just leave iCloud photos turned off on the Mac and just use AirDrop to send over new photos as a temporary solution. Then at some point go ahead and just start a scratch library and redownload them all. I took a photo just to do a quick test to send the photo over from iPhone to Mac to confirm the ease of transfer, metadata, etc. Fully expecting a dead simple process but before I could send the photo over it popped up on the Mac Photo library. I looked. I blinked. I laughed. Then I deleted a couple of garbage photos on the iPhone that I recently took to share something in Messages. They disappeared from the Mac a minute later. Took another photo on the iPhone and it popped up on the Mac.

At this point I looked in Photos preferences on the Mac to confirm that iCloud photos was not on… the state I left it in yesterday when I was prompted to purchase more storage. Okay, iCloud photos is off as I left it. But it’s updating as if it were on.

So, I guess for now I’ll leave it be. I have no idea what to make of it.