Which way does iCloud Photos Library sync work?

[subaiku]

Hi guys, got a photos library dilemna. I have over 100k photos currently in my photos album. Thing is I now want to sync it to my Macbook. I had an older backup of the photo library (which only has 50k photos) which I transfered to my Macbook. My thinking was it would save time redownloading everything again from the cloud.

I haven't checked the 'iCloud Photo Library' option yet in the preferences as I am unsure which way the syncing would go? Would it update my Macbook with the current photos or would the older library on my Macbook override the one on the cloud?

 

[jagolden]

Good question! Following.

 

[FreakinEurekan]

Both ways. If the photos on the Mac are all on iCloud, your best bet is to start with nothing, and just let it download. If you have 50k on the Mac and 100k on iCloud, it’s gonna take exponentially longer to compare all 50k and merge the libraries. Which would be fine if it needed done, if say only 20k of them were dups. But if all 50k are dups, get rid of them and let it do it the simple way.