Importing an external Photos Library into the System Photos Library

tperryh wrote: …The repair worked and it is fine. Can you tell me how to run a repair function on the file.

To repair a Photos Library, close Photos and re-launch by option-command-clicking the Photos app icon. This does not operate on a file-- it repairs the Library with its database.

For #2 above, if I make the library I am trying to import the System Library, will I lose the album and folder designations from the original System Library in favor of those designations on the external drive?

I don't know what that means. The new Library will have the same organization as the iCloud Photos Library. iCloud makes all the connected Photos Libraries exactly the same as iCloud Photos. iCloud Photos is all about synchronization. (Of course, some devices don't see all the features of Photos-- iOS doesn't see keywords, TvOS doesn't have editing.) If you connect an new Library to iCloud, no pictures or albums are deleted-- the Libraries are merged.

Also, will I need to move this System Library back to the Mac drive? The problem here is the Mac drive has only 256 GB capacity.

You should use the external drive for the System Library. The Photos Library works fine from an external drive. A 256 GB hard drive on your Mac is just enough to hold the Operating System and a few often used files. You need a fast APFS formatted SSD for most of your stuff, including Photos and music.

I've set the System Library on the Mac to optimize storage which shrinks it to 15 GB on the Mac while in iCloud the library is 389 GB. The library on my external drive is 254 GB.

The 16K pictures in my connected "Favorites" Library takes 120GB at iCloud and 150 GB on my Mac. I've been editing a lot lately, so the extra is probably in temporary preview images. Using Optimize Storage make is impossible to backup your pictures.

Is the trick then to optimize the storage of the Library on the external drive after designating it as the System Library and then copy it back to the Mac drive?

Optimize works by keeping only screen-sized images local and depending on iCloud for the full sized versions. When you edit or print a picture, the full sized version must be retrieved from iCloud. When you back up an Optimized Library, you only back up the smaller versions-- it's not a true backup. You should be keeping one version on some device, usually the main Mac, that is not optimizing, but rather it downloads and keeps the Originals:

Then you use another hard drive to run Time Machine (or an equivalent) to keep incremental backups of the Library.

See this:

Make a New System Library connected to iCloud

What léonie said, and a warning: If this drive is in a an incompatible format, stop running Photos with it immediately!  A Photos Library can sit on an incompatible drive, but running it may corrupt the database.

Is there a reason that you don't want to repair the Library? It's not unusual to need to repair a Library from time to time, even if it seems to be working. Photos may find inconsistencies that aren't so apparent. That why we go to the doctor after all--not just to fix what's wrong, but she may find something we hadn't know about!

When you use File>Import to merge Libraries, you lose all the albums and folders that you may have used to organize those the picture in that Library. There are two ways to avoid this:

#1 You can use the trusted 3rd party app PowerPhotos ($40) to do the merging and it will maintain the established structure of folders and albums. It does lots of other useful stuff, too.

#2 You can use iCloud to merge the two Libraries. You can just switch the System Library designation to the other Library, and iCloud will import all that stuff for you to iCloud Photos. It will then transfer everything that was already in iCloud Photos to the new System Library, so that they will both have all the pictures with the same structure. Of course, you'll need to make sure that you have enough room locally (on that properly formatted drive, I guess) to hold all the pictures.

Either method will check for duplicates in the merge, and it will avoid exact duplicates.

What do you think?

Is the external drive fully compatible with Photos for Mac? It needs to be prepared exactly as described here: Move your Photos library to save space on your Mac - Apple Support

The drive needs a wired connection, not a network connection, the filesystem format needs to be macOS Extended (Journaled) or APFS, and you should be able to set the "Ignore Ownership on this Volume" flag.

If the library is on an incompatible formatted drive as you've been warned about download the free version of PowerPhotos and see it if can read the library. I can "open/read" libraries without them being opened by Photos.

If you can see the external library and all its files and albums and folders you can use the paid version of PowerPhotos to merge the external Library into your main library. This user tip shows the differences in a merge by PowerPhotos and an import by Photos: Merging/Importing iPhoto/Photos library into Another Photos Library: PowerPhotos vs Photos

As alway, beside you have a backup copy of your primary library before attempting any import or merge.

APFS is a newer format that is very efficient and quick, taking advantage of peculiarities of sold state drives. But Mac OS Extended (Journaled) is fine.

If you're curious about the drive, you can run First Aid with the Disk Utility app, and it will check it out. This is not the same as the Library database being error free, though. You should rebuild your Photos Library--close Photos and re-launch by option-command-clicking the Photos app icon. If you use iCloud Photos with this Library, it’s possible that this will cause a re-sync that lasts long enough to make you nervous.

tperryh wrote:

...

For #2 above, if I make the library I am trying to import the System Library, will I lose the album and folder designations from the original System Library in favor of those designations on the external drive? Also, will I need to move this System Library back to the Mac drive? The problem here is the Mac drive has only 256 GB capacity. I've set the System Library on the Mac to optimize storage which shrinks it to 15 GB on the Mac while in iCloud the library is 389 GB. The library on my external drive is 254 GB. Is the trick then to optimize the storage of the Library on the external drive after designating it as the System Library and then copy it back to the Mac drive?

Importing a library into another library has a few important limitations, if you do it using the Import > Library command built into Photos. Merging Libraries with PowerPhotos is more versatile.

• Limitation 1 - The structure and keywords: The Photos.app can only import the media directly from another library. When importing directly from another library edited items will be imported as a pair of the original and the adjustments, which is great, but the keywords will be missing, which is disappointing. And the structure of the library cannot be imported. We cannot import the albums and folders, they will be lost.
• Limitation 2 - No import from an iCloud Photos Library: We cannot import from a library that is syncing with iCloud. we can import photos and videos from secondary libraries into our iCloud Photos Library, but not from an iCloud Photos Library into an external archive library.

With the full, paid version of PowerPhotos both limitations are no problem - we can import from our iCloud Photos Library into other libraries, we do not lose the keywords, and we can copy albums and folders into another library. It is much more versatile.

Oh-- it occurs to me that I should make the point-- I said,

The 16K pictures in my connected "Favorites" Library takes 120GB at iCloud and 150 GB on my Mac

We can't think of the Library size as static-- the size expands and contracts as we use it. You need more room that that number you see might suggest.