Difference between Disk Utility & Finder

[MultiFinder17]

Howdy all, I've been stumped by this issue for the past few days. I've been trying to partition the SSD in my Air (11" 2011, i5, 2GB, 128GB, El Cap) evenly, as I only have about 45GB used and I'd like to try out some other versions of OS X on it. However, Disk Utility refuses to shrink the main partition down below 70GB or so. Looking in Disk Utility, it seems to think that I only have about 50GB free rather than the 75GB that the Finder thinks I have. Any idea how to explain this 25GB difference?

 

[casperes1996]

I can't remember if El Cap was before or after the concept of "purgeable space". If it's after, this is a theory:

Finder reports how much space you've got available to fill up with files.
Disk Utility reports how much space is free on the SSD.

Sounds similar, but isn't. If you've got data on your SSD that also exists in iCloud, like photos and documents, Finder will cateegorise this as purgeable space. Even if it removes it from the hard drive to make space for something else, you'll still have access to it. Disk Utility will just count it as used space, since it's on your drive.

There's also the possibility of local Time Machine backups. Again, since the backups exist on a separate drive, Finder will see it as purgeable space, whereas Disk Utility will report it taking up space, because it does.

 

[chabig]

There are files that take space which is not reported by the Finder. For example, Time Machine makes local backups when you're not connected to your normal Time Machine volume. Though these files take space, they get deleted if the space is needed for something else. Thus, Finder doesn't report that space is being used.

There is not reason you need equal sized partitions if you just want to play around with other macOS versions. Just make the second partition 40GB and run with it. That should be large enough. Better still, but an external drive and use it instead.

 

[MultiFinder17]

I appreciate the info! I've already disabled local snapshots for Time Machine, which did free up a bit of space. However, the biggest difference that I'm seeing is that it sees around 43GB of Apps, while I cannot for the life of me find anywhere near that much space used by Apps. I don't have Steam or anything that should be storing Apps in the Library folder or anything on here, and the Applications folder is only around 10GB.

On the plus side, after turning off the local snapshots, Finder and Disk Utility are finally in agreement, just with a number that's higher than it should be

 

[casperes1996]

I appreciate the info! I've already disabled local snapshots for Time Machine, which did free up a bit of space. However, the biggest difference that I'm seeing is that it sees around 43GB of Apps, while I cannot for the life of me find anywhere near that much space used by Apps. I don't have Steam or anything that should be storing Apps in the Library folder or anything on here, and the Applications folder is only around 10GB.

Well, glad that local snapshots at least helped.

If you go to System Information and you open the "Applications" tab, you'll get a list of all that the system categorises as "apps". You'll find it includes more than what you might think.
Even something like "AskPermissionUI.framework" technically goes under the category of apps.
Based on your screenshots, it does look like the difference between your Applications folder and the Apps category is rather big, but then again, I don't really know what hides on your system
You could use something like DaisyDisk or Disk Sweeper or what they're all called to get an easier overview of large apps on your system, whether or not they're in the Applications folder or elsewhere

 

[MultiFinder17]

Finally got to the bottom of it! Turns out to be that good ol' HFS+ joy. Disk repair did the trick and gave me back my missing 15GB, so now it's only reporting 50GB used, right where it should be

 

[casperes1996]

Finally got to the bottom of it! Turns out to be that good ol' HFS+ joy. Disk repair did the trick and gave me back my missing 15GB, so now it's only reporting 50GB used, right where it should be

Hm, right, ok then. I've had corrupted permissions on HFS+ and incorrect sector counts, but it's never resulted in Disk Utility showing the space as "Applications" - Whatever, glad you got it fixed.

 

[MultiFinder17]

Yeah, same here. Either way, I'm glad I managed to sort it out.

As for the reason I wanted a same-sized partition, I cloned over my current install of 10.11 and upgraded my original to 10.13. That way I can see how High Sierra runs on this machine with my current setup while having the option to easily go back. So far so good; I'm impressed at how seemingly decently it runs with only 2GB of RAM.