How much disk space do I really have?

Question

Level 1

16 points

How much disk space do I really have?

Recently, I wanted to upgrade my OS as I am still stuck on Big Sur. Turns out I did not have enough disk space on a 500GB SSD to complete the installation. I used the app Grand Perspective to find the low hanging fruit, and I got rid of well over 30 gigs of large video files. But here's the thing, when I look at About This Mac > Storage, I still only see 7.47 GB free which is impossible given how much I just got rid of (yes, I emptied the Trash). There are two confounding factors. First, currently I'm seeing over 200GB taken up by "Other."

Second, using Grand perspective shows only 354GB used.

I also just got rid of yet another 24GB thanks to upgrading Backblaze to a recent version. It's still showing only 10GB free , and now GrandPerspective shows only 330GB used. And I still cannot upgrade. At this rate I will never be able to do the upgrade.

Any idea what's going on here? There is no way I don't have enough free space, but for some reason, my OS and the installer are convinced that I don't.

MacBook Pro (2017 – 2020)

Posted on May 20, 2024 9:12 AM

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Answer 1

HWTech

Level 9

56,402 points

May 21, 2024 8:45 AM in response to tobogranyte

FYI, macOS is showing you 7.47GB of Available storage.....this may or may not be actual Free space, but may consist of "Purgeable" space instead. It is unfortunate that Apple chose to use the term "Available" nearly everywhere in macOS when it is so misleading. Most likely you may have storage consumed by an APFS backup snapshot which may still contain the data you just deleted. See my other post where I explain the storage terminology in a bit more detail:

macOS Storage & storage terms explained -- hwtech - Apple Community

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Answer 2

tobogranyte Author

Level 1

16 points

May 20, 2024 9:48 AM in response to tobogranyte

I have partially solved this. Guess how? I restarted. After doing so, I immediately went into About This Mac > Storage. It started at around 10GB free and then rapidly began updating and seems to have settled at 105GB free. That still doesn't match what I'm seeing on Grand Perspective. But I'm pretty sure I can upgrade my OS at this point.

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Answer 3

tobogranyte Author

Level 1

16 points

May 21, 2024 10:14 AM in response to HWTech

Thanks for that @HWTech. Indeed, it's a confusing topic. Fortunately, after my restart (see my other comment) the numbers changed radically showing much more "Available" space and I was then able to do my update to Sonoma. The numbers I continue to see in the new Storage area of System Settings are still off from what Grand Perspective shows me, but they are in the same ballpark. I will just live with that until the next time I start bumping up against free storage requirements for other reasons.

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Answer 4

Ronasara

Level 6

14,679 points

May 20, 2024 10:25 AM in response to tobogranyte

Periodically the Mac will remove some of the "other" data. We cannot control this. The only reliable way to know how much storage is used is to use Disk Utility to see this.

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