How do I move my photos library to an external drive?

So I think I solved this and it was MUCH easier than I expected based on the responses you've received. I had 50K+ photos and needed to free up space on my old iMac which I use for my local copies of the photos. I simply bought a 4TB hard drive from the apple store for ~$150, connected it via USB, and then held down the option key when launching photos. This prompted me to setup a new primary Photos library which I did on the new external drive. I then launched photos and started to re-sync my machine to the iCloud library. Yes, it's taking a while (days) to synch, but I just leave the Photos app open and it works.

I also ported my old iPhotos library to the external drive (I wanted to keep the library just in case there were some dependencies there between Photos and iPhotos and this whole thing went sough). This was interesting. According to Finder the iPhotos library was ~350GB (really big) but when I moved it to the external drive it only ended up being about ~150GB. So somehow Photos knows how to disentangle itself from iPhotos if necessary. This helped free up a lot of space and the entire Library has remained intact on iCloud and synching to my new hard drive. Next step I'm going to move the original Photo's library from my iMac to free up another ~400GB.

BTW...the iMac is now running great with the free space and Sierra. It's re-optimized the drive and back to a usable machine. I hope this helps.

I know it's a long time, but I'm a very new mac user and I can follow step one, but cannot find how to do step 2 Copy the Photos Library from your Pictures Folder to the External Disk.

Where do I go to find the photo library? I went to the finder, but it doesn't list Photo library or pictures folder. We have a newer mac. bought jan 2015.

Thank you

Hard Disk -> Users -> Your Name -> Pictures

Thanks for this info. I used it with Sierra and it looks like it worked! I haven't deleted the one internally...a little nervous about doing that! But from now on new photos will go to this external disk. Yay!

Yeah...I would hold onto the old iPhoto and Photo library files at lease until you're comfortable. I tried moving just the old iPhotos file to a separate drive and it appeared to work...but I'm still a bit concerned about the iCloud photos integrity.

When I go to the Photos app, then Preferences and under General, it won't let me click Use as System Photo Library. Am I doing something wrong?

Think you have to hold down the option key when launching Photos...

Designate a System Photo Library in Photos - Apple Support

BTW...you'll need to launch Photos and then stop you MAC from sleeping if you want to accelerate the iCloud import to the new System Library. I found that my update was taking 10x longer than expected simply because the Photo app was sleeping when the Mac was not in use.

When I go to the Photos app, then Preferences and under General, it won't let me click Use as System Photo Library. Am I doing something wrong?

No. That means the library is the System Photo Library.

That makes sense. So, how do i change it so that a different library is the System Photo Library?

Open the other library and then you'll have the option to select.

Can you tell me how to undo this change as I would like to go back to before I chose the entire mac library to save to hard drive..

Can you tell me how to undo this change as I would like to go back to before I chose the entire mac library to save to hard drive..

Drag the Photos library back from the EHD to the pictures folder of the Mac and double click on it to open it and set it as the default location

LN

What format is the EHD? For Photos it can only be Mac OS extended (journaled), not used as a Time Machine backup volume and connected with a fast wired connection

LN