Mac Mini Photos app extremely slow with external HDD library

There are lots of advantages to having a smaller "Favorites" Library in addition to the large Archive Libraries.

The ability to keep our Favorite pictures on the internal drive, as léonie mentioned is maybe the greatest advantage.That's especially important for laptops (like my MacBook and my MacAir) and for mobile devices (like my iPhone and my iPad.) Having the System Library kept internally is nearly a requirement for MacBooks.

I use iCloud Photos to keep my devices' Libraries all synchronized, and with a smaller Favorites Library I don't need so much iCloud Storage space--just three bucks a month does it for me.

Searches are faster and more efficient. Even though I use lots of Albums and Folders, and I add lots of keywords and captions, it's way easier to find the pictures I want without having to scan through hundreds of hits to my queries.

I need to back up my Favorites Library often, as it changes often. But the Archive Libraries don't need backing up so much. Time Machine on SSDs can easily take care of the Favorites, and the Archives I just to external drives (like those 10TB HDDs I have) much less often-- and for those I don't mind the slowness.

I say Archive Libraries, plural, because I have divided them up, with some overlap. I have an iPictuers Archive, a Work Pictures Archive, a Nikon Archive, a Wife's Old Family Pictures Library, a My Old Family Pictures Library, (because I can't remember who people like Uncle Lemuel belongs to,)and a few Archives before and after major life events.

WhenI started this, I duplicated my one Library, and then I went about removing the non-favorites from it. It's way easier to be sure of non-favorites than of favorites. So after the first run-throughs, I continue to eliminate pictures that see redundant or just aren't images that I want to see over and over. All the pictures in Favorites are also in some other Archive Library. This is how I used keyword "quick-picks" to help:

Choosing Favorites using Keywords in Mac Photos - Apple Community

For handling multiple Libraries, most of us use the trusted 3rd party app PowerPhotos ($40.) PowerPhotos makes it easy to move pictures, albums, and folders between Libraries while preserving the metadata and organization. It also has lots of other features, like advanced Duplicate searching, batch editing of photo metadata, and searches through multiple Libraries. They offer a free trial version.

It would affect your iCloud Photos Library and the Media Browser. As you probably know, only one library can be your System Photos Library (visible in the Media Browser and other apps) and can sync with iCloud Photos between your devices.

But it has its advantages:

• I am keeping only the photos and videos that still need editing and I am currently working with in my System Photos Library, plus all photos I am always want to be accessible, mostly the photos I selected a favorites. This includes old family scans and important old documents.
• My System Photos Library is now small enough to fit onto the internal drive of my all my Macs and I can use it on my iPhone and iPad without being forced to use "Optimize Storage", so all items are always locally available, even when I do not have an internet connection. I can simply copy the library to have a backup, because it is not optimized. And Photos is much more responsive. It is easier to find important photos, because only the favorites are in the library, not hundreds of slightly different versions of the same photo.
• On the external drives is an archive of all photos, split across several smaller libraries, plus aa backup of the archive libraries.

Do you really need all 3.5TB of photos in the same library? You may want to consider to split the library into smaller libraries.

I noticed that Photos became quite slow after my library became larger than 50000 items. Every action that involved the complete library become somewhat slow - searching the library, updating smart album, etc. Whenever I upgraded the system to a new version where the Phots.app needed to scan the library again, I had to wait for more than a week before Photos became more responsive.

The Photos.app is not a professional app like Aperture has been. It can work with huge libraries, but not gracefully.

You have a Mac with a powerful processor, but the Photos.app is needing a lot of processing power to analyze the library. It is trying to understand what a photo or video is showing - not only recognize the objects but to understand the events and how the photos are related.

You may want to check, if you are encountering the same problems, if you create a small Photos Library for testing. If a smaller library with just 50000 items is working better on your external drive, consider to split your archive library into several smaller libraries. It will make it much easier to manage the archive. even just copying the archive to a backup drive will be faster.

smithrog34 wrote: Current HDD with USB-C into a back port crawls and beach balls all the time, especially when opening.

I have some 10 TB mechanical drives that I use for archives-- they are terribly, painfully slow. Ten years ago their speed might have been thought OK, but now I wouldn't use them for anything that I couldn't wait for.

SSDs can die. Everything I back up is going to at least two drives. Then periodically I use those 10TB archives

Buy only quality SSDs. They now cost twice as much as a couple of years ago.

I use Blackmagic Speed Test (free!) to compare the speeds of drives.

I watched an old Law & Order (they're so great!) the other day, and the detectives were really impressed with the technology when they found that the victim had a souped-up computer with a 25 GB hard drive !

smithrog34 wrote: …100% of my images are imported to my M4 MacBook Air, then synced via iCloud to the Mini. If the Air has to have a library on the internal drive, how would the multiple libraries work with my setup?

Same as now, I think. You import the pictures to the Favorites System Library on the MacAir. They will show up in the Favorites System Library on the Mini. You edit them, choose the Favorites (and non-favorites) and then send them all to the Archive on the external drive. You then delete the non-favorites from the Favorites System Library.

This sounds similar to what léonie says that she does. Since I edit pictures on the same Mac I import them to, it's a little different for me. I import my Nikon pictures to a Nikon Recents Library that I keep on my MacBook Pro with a 2TB drive. I edit them in the Nikon Library (and Lightroom,) and then I choose the favorites, all this on the MacBook. Then I use PowerPhotos to transfer those to my Favorites Library on the MacBook, and iCloud copies them to my other devices.

Because I'm a bit obsessive about losing pictures, the Nikon pictures are saved in Finder Folders and are transferred to Archive drives withhout having moved through Photos at all.

As I had said, the process is mostly "Same as now." The difference from the usual process is that, instead of backing up a humongous file every time, you backup a small Favorites Library, and then you move the new pictures from your System Library to your Archive Library. Later you can delete the non-favorites from the System Library and keep it small.

But it is a lot more tedious to have to deal with a huge library. Just consider:

• Copying a huge library to an external drive can take hours, even fail because of problems with the external drive
• Having to upload a huge library again to iCloud Photos can take weeks
• Searching photos in a huge archive will be slow, also updating smart albums
• Updating or upgrading or repairing a huge library is usually taken a very long time and needs a huge amount of free storage on the same volume.
• And we may need additional free storage in iCloud, if we need to sync an existing library again with iCloud. iCloud Photos is using the worst case assumption, that all items in our library are different from the items already in iCloud, when it is syncing a library with iCloud. So, if we are having a 4TB Photos library in iCloud Photos, disable iCloud Photos, then turn it on again, iCloud may refuse it, if we do not have 4TB of free iCloud Storage.
• A small favorites library is easier to use on devices with small displays, for example an iPhone. It helps to have only an essential subset of or photos on the mobile devices.