Recently I started constantly getting warnings on my MacBook Air about the hard drive almost being full. This despite clearing so much stuff from it. iTunes library and content on an external drive. Photos libraries on an external drive. I've configured Photos to use the library on the external drive as well. Still, when I right-click the local hard drive on the MBA (120 GB SSD), it shows Photos is taking up 92 Gb. That explains why the disk would be almost full--except those Photos are in a library on an external drive, not the local drive. Right?! I can't figure out what is going on. Why is Mac OS apparently telling me that a photo library on an external drive still counts against my local hard drive space? It's getting so that this is unusable since I'm down to < a few hundred Mb. I am using iCloud, and I do have Photos configured to "Download Originals to this Mac". However my understanding is that any photos would still be stored in that library on the external drive and therefore not take up space on my main HD.