iCloud Photo Library doubled the size of my library

Hi - iCloud does not normally require more space.

Have you used iCloud photos in the past, on this or any other device? Ie Is it possible you have previously stored images there that have now been merged with your library?

If the sync is still going on, it is possible that the library will grow while it is syncing, but that should be temporary.

And I understand from your post that you have the library on an external drive. If so, is it correctly formatted (an incompatible format for a drive can cause all sorts of strange behaviours with a photos library). Normally when you buy a new drive it will be formatted ExFAT (a microsoft format) which is not compatible with a photos library, and needs to be reformatted on the mac first.

It must be formatted APFS or MacOS extended (journaled) (preferred for spinning drives)

It Must not be (or have been) used for time machine. (A time machine drive can be used if re-formatted first)

It must have the 'ignore ownership" checkbox ticked.

It should not be on a memory stick, SD or similar.

It must also not be a network drive (a direct connection is required - eg USB or Thunderbolt).

File sharing services such as iCloud Drive, Drop box, Onedrive etc are not compatible with Photos libraries.

It stands to reason that if you want any sort of reasonable performance it should be a fast drive with a fast connection.

See

https://support.apple.com/en-gb/HT201517

pnwruddyman wrote:

It appears to have eventually resolved on its own, some time after the full library uploaded. It reached double the size of the original library at one point. Apple needs to alert users to this possibility, because large photo libraries can easily exceed storage, especially if doubled! It's even trickier for you! I copied my bloated library to another disc and it eventually shrunk back to normal.

Which system version is running on your Mac? The amount of additional storage may depend on the system version.

In the early versions of Catalina the Finder did not update the size of the Photos Library immediately and correctly. Sometimes the Finder has been showing a size that is much too small, sometimes a size much too large. This has been fixed in Big Sur.

But a library may indeed grow, when you start syncing with iCloud Photos, if there are already photos and videos in iCloud. Photos will upload your current library and merge it into the existing iCloud Photos Library, while trying to avoid duplicates. Photos can only detect exact duplicates. If Photos cannot recognise a file as duplicate, you may need more storage than before. And temporarily, while the library is being rebuild, the library can grow considerably in size.

And when the library is syncing back from iCloud, the files will download as new files. This may break space saving hard links to similar files on your Mac. If you are still having an old iPhoto Library, remove it from your system volume. With iCloud Photos enabled the old iPhoto lIbrary and the Photos Library created from it can no longer share the storage for identical images in both libraries. The downloads from iCloud are no longer hard links to the iPhoto originals and the iPhoto Library plus the Photos Library will now need twice the storage for the original image files.

To check format and ignore ownership you can open the drive info pane (right click "get info" or CMD-i) as shown in the screenshot.

I fully agree that sometimes apples info on the detailed workings of some stuff is lacking.

Were you ever able to solve this? Was replacing your 1TB drive sufficient to hold the expanded library? If so, did the library return to its original size once it had uploaded and synced? I'm encountering the same issue. Unfortunately, the library is on an internal SSD that can't easily be upgraded.

Thanks. That's what I suspected. I wonder if it's worth copying to a larger drive and uploading it from there. Maybe I can just copy it back to the original drive once it's settled back to its original size? Do you think iCloud syncing will just pick up again like nothing has changed?

I'm running Big Sur on this particular Mac.

I just copied the directory to a 2GB external USB drive, and turned on iCloud Photos. It's a rotational drive, so Photos is not nearly as responsive as I'm used to. Here's hoping!