Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.


macrumors newbie
Original poster
Nov 1, 2019
I have a MacBook Air, 256B, which replaces machines I have had in the past which have always had a lot more hard drive space.

However, the photos I have in my iCloud would almost fill the hard drive so I am currently using the optimise space function which is working fine.

I would still prefer to keep a physical back up of all my photos though so have been trying to work out the best way to do this.

From the research I have done, the following solution would seem to work - leaving me with a library optimising space on my MacBook Air which I can use day to day, then a back up on an external drive which I can back up to every now and again.

I would be grateful for anyone telling me if this isn't the case though, or if they have any better solution...:

1 - Set up a new library in Photos
2 - Copy new library onto external drive
3 - Set new library as system photo library (I think I would need to do this to be able to make use of iCloud and do the next step)
4 - with settings in Photos set to download originals, open the Photos app - all photos should now download from iCloud onto the external hard drive photo library
5 - eject hard drive
6 - set old library back to system photo library
7 - go through the same process (apart from steps 1 & 2) to back up each time

Can anyone see any flaws in this? Am I likely to run into issues changing system photo library all the time?


macrumors newbie
Original poster
Nov 1, 2019
Thanks - yes, I've looked at that one. However, it doesn't really deal with the question of having 2 libraries and effectively using them both for iCloud, but in different ways, to achieve a space optimised version of your library on your laptop and a fully downloaded version on an external hard drive.


macrumors 601
Aug 28, 2012
Between the coasts
You can have only one designated System Library at a time (per Mac). You'd have to switch the status of those two libraries in order to sync each of them to iCloud Photos. This Apple article provides additional info:

I can see doing this occasionally (as you described) in order to get the kind of full backup you desire, but each re-sync to iCloud will likely take a good bit of time, as the process compares the newly-added library to the iCloud-based library to avoid duplicating images.

One potential unintended consequence could involve images you've deleted from iCloud, but which remain in the "keep originals" library you use for backup. I expect those images would be treated as new images and re-added to iCloud the next time you connected the backup library to iCloud. The apparent behavior when connecting a library to iCloud is "merge" - identify duplicates, add anything that is not a duplicate, delete nothing.


macrumors 601
Feb 15, 2008
Try setting up a secondary account on your MacBook Air. Sign into that with the same iCloud account.

If you can do that (I'm 99% sure it's possible to sign into multiple accounts on the same Mac with the same ID, as you would be able to with separate installs, but it could be a limitation)... then you don't have to mess with the settings on your main account but can set up the library on the external under the second user account. Log into it from time to time to keep the "backup" up to date. But also have a backup strategy which makes backups of this library (time machine or otherwise eg CCC) because your plan won't result in a backup in itself, just fancier copies of what exists elsewhere.
  • Like
Reactions: ApfelKuchen


macrumors G3
May 31, 2007
Florida, USA
Using a second login account on your Mac with the library on an external drive is probably the best way to do this like said above.

That said, could you maybe set up one of your previous Macs (it doesn't have to be high end, just a desktop machine, or a laptop you can keep in one place) as a NAS? You can use it as a Time Machine backup target, and you can have an account set up on it that syncs your iCloud Photo Library and iCloud Drive with optimized storage off so you get a full copy. Since it would just sit in one place, keeping external drives connected wouldn't be a big deal. This would likely solve your problems and provide a good place to store backups of your data.
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.