How to use iCloud to help manage Photos libraries too large for an internal Mac drive

In a recent column, “How to cope with a Photos library too big to fit on an internal Mac drive,” I explained that there aren’t any methods supported by Apple that let you have a Photos library at full resolution on a Mac if the library can’t fit on your internal drive with the spare room you need—or exceeds the drive entirely.

Macworld reader Matt wrote in with a terrific workaround that offers an approach much closer to what other readers were looking for: one copy of a Photos library set up with iCloud Photos that’s only thumbnails and stored on your internal drive, and a second iCloud Photos-linked copy that’s linked to an external drive.

Matt’s idea relies on how macOS lets you create multiple accounts, each of which can be uniquely linked to an iCloud account. However, it’s also possible for two accounts or more to both link to the same iCloud account.

Normally, you wouldn’t want this, because it would mean syncing the same data in two places on your startup drive. But with the way in which iCloud Photos and Photos for macOS works, it’s a nifty solution.

Here’s the schematic of how to make this work:

1. Attach an external drive with sufficient storage for your full iCloud Photos library at full resolution. (You can find this number at log in, click the Settings icon, and hover over the Photos and Videos section of the Storage usage bar.)

mac911 storage of photos icloudIDG

Use to get the full-resolution size of your iCloud Photos library.

2. Next, create a second macOS account called, for instance, yourname plus photos, via the Users & Groups preference pane.

3. Log into that macOS account (optionally using Fast User Switching), open the iCloud preference pane, and log into the iCloud account used with your main macOS account and with iCloud Photos.