Freeing Up ~180GB By Rebuilding The Spotlight Index

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If you’ve ever opened System Settings > General > Storage on a Mac and stared in confusion at a “System Data” category that’s somehow 200GB+, you’re not alone. It’s one of the most common (and most opaque) macOS storage complaints, mostly because APFS uses copy-on-write and shared blocks, so there’s rarely a single tidy folder you can point to and delete.

A useful troubleshooting writeup popped up on r/MacOS recently where a user tracked down their own runaway System Data figure — and the culprit turned out to be an oversized Spotlight index. In their case, System Data dropped from roughly 260GB down to 83GB, freeing around 180GB of usable space. Here’s the gist of how they found and fixed it, plus a bit of context on why it happens.

Why “System Data” balloons in the first place

Before diving into fixes, it’s worth ruling out the obvious culprits first: browser caches, app caches under ~/Library/Caches and /System/Library/Caches, and old iOS/Time Machine backups. Cleanup apps and manual cache-clearing often only recover a few gigabytes, which won’t move the needle if the real cause is something else.

Step 1: Rule out deleted-but-still-open files

Sometimes a running process holds a deleted file open, so the disk space never actually gets reclaimed even though the file no longer shows up anywhere. You can check for this with:

sudo lsof +L1

Look through the output for entries marked (deleted) with a large size next to them. If nothing stands out, move on to the next check.

Step 2: Check the size of the Spotlight index

This is where the real problem often hides. Spotlight’s search index lives at:

sudo du -sh /System/Volumes/Data/.Spotlight-V100

A healthy index is usually a few gigabytes. If this command comes back showing tens or even hundreds of gigabytes, you’ve likely found your System Data bloat — commonly concentrated in the index’s Store-V2 subfolder. This tends to happen when Spotlight tries to index very large or unusual folder structures, such as huge cloud-sync libraries of photos or design files.

You can also check whether indexing is currently enabled or stuck with:

mdutil -s /
mdutil -s /System/Volumes/Data

Step 3: Rebuild the index — don’t delete it manually

The safe way to fix a bloated Spotlight index is to let macOS rebuild it from scratch, rather than manually removing system directories with rm -rf (which risks breaking Spotlight or worse). The command to trigger a rebuild is:

sudo mdutil -E /System/Volumes/Data

This erases and rebuilds the index. Depending on how much data is on your drive, this can take a while, and you’ll likely notice higher CPU and disk activity while it’s working. Storage numbers may also fluctuate temporarily during the process — that’s expected.

Step 4: Confirm the fix worked

Once indexing has settled down, re-run the size check to see the new index size:

sudo du -sh /System/Volumes/Data/.Spotlight-V100

And head back to System Settings > General > Storage to see whether System Data has dropped and free space has returned.

Quick checklist

Note your current System Data size and free space
Run sudo lsof +L1 and check for large (deleted) entries
Run sudo du -sh /System/Volumes/Data/.Spotlight-V100 to check the index size
If it’s oversized, rebuild it with sudo mdutil -E /System/Volumes/Data
Wait for reindexing to finish, then re-check both numbers

Worth noting: this fixed the issue for that particular user, but System Data bloat can have other causes too — old system snapshots, orphaned VM images, or leftover update files, for instance. If a Spotlight rebuild doesn’t move the needle for you, those are worth checking next.

Adapted from a writeup shared on r/MacOS.

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Freeing Up ~180GB on macOS by Rebuilding the Spotlight Index