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  "path": "/blog/recover-missing-disk-space-on-osx",
  "publishedAt": "2026-06-06T11:16:00.000Z",
  "site": "https://jeremycherfas.net",
  "textContent": "I had a lot of trouble on my Mac with Time Machine telling me the disk was full and yet I could not find huge wins just by inspection and deleting things that looked too big. I drafted ChatGPT in to help diagnose the problem and it had me jump through all sorts of hoops, which did eventually recover the space I needed.\n\nRather than repeating all those steps as an _aide-memoire_ , I asked ChatGPT to go through the entire exchange and prioritise the various steps. This (lightly edited) is what I received.\n\n**Retrospective: Better Process for Identifying the Missing Disk Space**\n\nYes. In hindsight, once we saw the **large`df` vs `du`** discrepancy, rebooting should have moved much higher in the priority list.\n\nA better priority order would have been:\n\n  1. **Confirm real free space with`df`**\n\n         df -h /System/Volumes/Data\n\n  2. **Compare with visible file usage**\n\n         sudo du -xhd 1 /System/Volumes/Data 2>/dev/null | sort -h\n\n  3. **If`df` says \\~203 GB used but `du` only finds \\~119 GB, stop hunting normal folders**\n\nThat discrepancy was the crucial clue. At that point, deleting\ncaches, MobileSync backups, and Homebrew files was secondary.\n\n  4. **Check for snapshots and open deleted files**\n\n         sudo diskutil apfs listSnapshots /System/Volumes/Data sudo lsof +L1\n\n  5. **If snapshots are mounted/protected/busy, reboot early**\n\nThe moment we saw: `/Volumes/com.apple.TimeMachine.localsnapshots/... ` and later `Snapshot ... Purgeable: Yes` a reboot should have been recommended as the quickest practical next step.\n\n\n\n\nSo yes: once the evidence showed **\\~80--100 GB missing from normal filesystem accounting** , the best path was:\n\n\n    df/du discrepancy → check snapshots/open files → reboot → recheck df\n\nrather than continuing to inspect ordinary folders.\n\nThe cache/MobileSync/Homebrew cleanup advice was still safe and useful, but it was not the main solution. The decisive clue was the `df`/`du` gap, and the decisive fix was rebooting to release mounted Time Machine local snapshots.\n\nI'm sure this will help future me. May it also help present you.",
  "title": "Recover missing disk space on OSX",
  "updatedAt": "2026-06-06T11:16:00.000Z"
}