Recently I've been beguiled by my local disk being almost full. This is on my everyday M3 MacBook Air running the latest Tahoe 26.2.

For years I've used Daisy Disk to debug space issues like this, it's great. In this case it showed the problem, but wasn't able to narrow down what the problem was nor remove it.

Not have any success through the normal means ("Googling around"), I wrote the developer of Daisy Disk, Oleg. They explained the problem and suggested a workaround. It worked like a champ! I included the explanation below and screenshots showing before and after.

I want to say thanks to Oleg for their help. And this is a nice opportunity to say thank you to indie developers in general who are often so helpful sharing their expertise. What a wonderful and important part of our community.

Oleg's explanation:

This error has recently been reported by a few other users as well, and our investigation shows that it's caused by a new bug in macOS, introduced in one of its recent updates. (It didn't happen before). The symptom is exactly like in your case - a Time Machine snapshot becomes damaged for unknown reason, and it cannot be deleted in the normal way - not only in DaisyDisk, but also not in Terminal, using the tmutil command-line tool. Moreover, the tmutil tool doesn't even list the damaged snapshot. It becomes almost entirely lost, while it still consumes disk space.

We have found the following workaround solution. Please launch the system's Disk Utility (/Applications/Utilities/Disk Utility.app) and in the left sidebar, select your data volume, likely called "Macintosh HD - Data". Note that there will also be another volume called "Macintosh HD" (without "Data"), but you should select specifically "Macintosh HD - Data". Then select the View \> Show APFS Snapshots menu command. In the lower part of the window, you will see the damaged Time Machine snapshot in the list. Please select it and then click the "-" (minus) button at the bottom to delete it.

And screenshots showing the before and after. Note the two broken snapshots in the list below.

After

Governments should produce public goods, like navigation aids and roads. That seems like a reasonable thing to expect of a functioning government, right?

I consider data a public good too. We all benefit from accurate maps, thorough measurements of the natural world, and trustworthy economic data.

Which is why it was I was so upset when I heard how the the current US administration has been on a tear to actually remove data. All through 2025, websites were taking down and datasets were taken offline. This Wikipedia page catalogs what's been happening, and this report by the American Statistical Association goes into more depth about what's been happening and its implications.

In response the Data Rescue Project sprang into action. They're a group of concerned academics, librarians, and citizens who have been copying and cataloging datasets so they aren't lost. The project's press page has links to many articles and presentations that describe their work and its impact. Last November I saw a call for volunteers for DRP on a mailing list of ex-Googlers and was eager to help.

Homeland Infrastructure Foundation-Level Data (HIFLD)

It's worth describing a bit about the particular dataset I actually worked on: Homeland Infrastructure Foundation-Level Data (HIFLD). It's a good case study.

HIFLD is a collection of maps. Maps of basic stuff, like roads, levees, river depth charts, locations of military bases. Beyond just being good maps, a big part of HIFLD's value is helping to make sure everyone uses the same maps.

So HIFLD is mostly curating data. Most of the data comes from other agencies (USGS, Army Corps of Engineers, Census Bureau) and HIFLD brings it together and provides it in a trustworthy, central place. Well, I should say "provided" because in September the government stopped providing it. The story is well told in this good article on Project Geospatial.

This is where the Data Rescue Project comes in. DRP volunteers immediately scooped up the data and kept in temporary storage. Then they organized a bucket brigade of volunteers to categorize and put snapshots into long-term storage. Importantly, this was coupled with metadata to ensure they're findable later. That's the part I worked on, uploading and entering metadata. We met our goal of getting all of HIFLD "rescued" by year's end. Frank Donnelly, the project manager, wrote up a nice summary of what we did and how. For my piece I relied on a nice Selenium driver, written by another volunteer, to create over a hundred projects (screen recording).

This is just one of many DRP efforts. Check out their tracker to see the breadth of work.

While I'm proud of this project, I keep reminding myself that we're playing defense. Having a one-time snapshot isn't nearly as good as having the government actually do its job. Which is why we need to keep demanding better leadership and a return to effective government. Assert your rights and protest!   ❌ 👑.