Move your Photos library to save space on your Mac
To save storage space on your Mac, you can move your Photos library to a different storage device.
Prepare your storage device
Make sure that your external storage device, such as a USB drive or Thunderbolt drive, is formatted for Mac: either APFS format or Mac OS Extended (Journaled) format.
You can't store your library on a storage device used for Time Machine backups. And to avoid possible data loss, don't store your library on a removable storage device like an SD card or USB flash drive, or on a device shared over your network or the internet, including over a cloud-based storage service.
Move Photos Library to the storage device
In the Finder, open the folder that contains Photos Library. By default, Photos Library is stored in the Pictures folder of your home folder. You can open your home folder by choosing Go > Home from the Finder menu bar.
Drag Photos Library to a location on your external storage device. Learn what to do if you get an error.
After the move is finished, double-click Photos Library in its new location to open it.
If you use iCloud Photos, or to access the library via the Photo Picker in other apps, designate this library as the System Photo Library.
If you want to delete the original Photos Library to save storage space on your Mac, you can drag it from its original location (the Pictures folder of your home folder) to the Trash. Then empty the Trash.
Always make sure that your storage device is turned on and available before opening Photos. If Photos can't find the device, it stops using the Photos library stored there and will create a new empty library at the default location (~/Pictures).
If you want to open a different Photos library
Press and hold the Option key while you open Photos.
Select the library that you want to open, then click Choose Library. Photos uses this library until you open a different one.
If you get an error when moving Photos Library
Select your external storage device in the Finder, then choose File > Get Info.
If the information under Sharing & Permissions isn't visible, click theto see more.
Make sure that the “Ignore ownership on this volume” checkbox is selected. To change it, you might first have to click the erase the storage device first.to unlock the setting. If the storage device isn't formatted correctly for Mac, or was used for Time Machine backups but hasn't been erased, this checkbox won't be present or won't be selectable after unlocking. In that case,
If you have some other permissions issue with your library, you might be able to resolve the issue with the Photos Library repair tool.