How best to attach multiple external SSD's so that Lightroom Classic can access and edit their data?

There is no additional configuration to do. All you have to do is add the photos to the catalog, no matter what mounted volume they are stored on. It’s as simple as this:

Drag a top level photo folder from any mounted volume, and drop it into the Lightroom Classic application window or icon. This is a shortcut to choosing File > Import, which you can also do.

In the Import dialog box, make sure Add is selected. This will add the photos to the catalog, without moving, copying, or converting them; leaving them where they are currently stored.

After they are imported, each separate volume containing cataloged photos will be listed at the top level of the Folders panel. All you have to do is click the triangle at the right side of any cataloged volume, to expand it and see all of the imported folder hierarchy within that volume. (In the example below from my laptop I labeled the internal volumes “containers” because they’re technically APFS containers, not partitions.)

---

@default90xwyqggy3p3 wrote:
When I have both SSD’s connected, will Lightroom integrate the pics on two separate devices into a single collection of Chickadee pics that span the old pics and the new pics?

---

Yes. When you select the All Photographs collection under the Catalog panel in the Library module, it will literally show all photographs on all cataloged volumes…even on volumes that are not currently mounted.

In addition – and this is where the real power of the cross-volume catalog comes in – you can create Collections that contains images from multiple folders on multiple volumes. Do you want to create a “best of” slide show or book containing your 50 best chickadee photos, but they are located across five external hard drives? No problem. Create a collection, and drag those photos from wherever they are into the collection. Because a collection is just a virtual list, this doesn’t duplicate or move any files. A collection is like a playlist in a music app.

This is also why it is usually much more powerful to create one catalog for all photos, not a separate catalog for each volume.

---

@default90xwyqggy3p3 wrote:
Or will I need to know when a specific picture was taken, find the right SSD on which that pic is stored, and then load just that single SSD to get the picture I want.

---

Because all cataloged photos across all volumes are listed in the All Photographs collection, when that collection is selected you can search for any photo you need using any method you want in Lightroom Classic (by filename, by date, by camera, by lens, by keyword, or any other metadata supported by the Find or Filter features). When you select the photo, in the Library module you can choose Photo > Go to Folder in Library, and the Folders panel will expand to select and show you the folder and volume that contains it. If it is on an unmounted volume, it will tell you that the original is not available; you can then of course connect its volume so that you can edit the photo.

If you want to go straight to where that photo is outside of Lightroom Classic, when the photo is selected you can choose Photo > Show in Finder/Explorer, and your computer will switch out of Lightrooom Classic to the desktop and open the folder that contains it.