1 person found this helpful
If you have copied all the folders of images to the external drive in exactly the same folder hierarchy of parent and sub-folders, then it is a very simple job.
1) Open Lightroom
2) Open the Folders panel
3) Highlight the topmost parent folder you can see. (eg. Pictures)
4) Right-Click and choose [Update folder location]
5) In the explorer/Finder window that opens, select the same (or similar) parent folder on the external drive.
Now Lightroom is linked to the photos and folders on the external drive.
Catalog is 'Internal', photos are 'External'
When you are sure all is well, the internal photo folders can be deleted, but you will still need another physical drive to backup the photos.
This is all better described in "Option One" at this link- https://www.lightroomqueen.com/move-photos-another-hard-drive-leaving-catalog/
2 people found this helpful
Agreeing with WobertC
You don't need a new catalog or a re-catalog. This would be totally the wrong thing to do, it is a mistake, it will cause more problems than it solves, it has a number of disadvantages; and it is also a waste of time and energy.
All you have to do is point the existing LR catalog to the location of the folders that contain the photos on the new hard disk. Follow his instructions, or the ones here: Adobe Lightroom - Find moved or missing files and folders particularly Figure 4 and associated text. This is an action that ought to take 30 seconds, at most, which is a lot simpler (and has a lot fewer drawbacks) than creating a new catalog and re-importing everything.