Why Spotlight will not find files on an external drive

You plug in the drive, search for a file you know is on it, and Spotlight returns nothing. The drive is mounted. The file is right there in Finder. Search just will not admit it exists. Here is why that happens, and the three causes worth checking before you assume the drive is failing.

Spotlight keeps a separate index on every volume

Your Mac does not keep one big index of everything. Each volume gets its own, stored in a hidden folder called .Spotlight-V100 at the root of that volume (what that folder is, and whether it is safe to delete). Your internal disk has one. So does every external you have ever indexed.

That design is reasonable. It means a drive carries its index with it, so plugging the same disk into a different Mac does not force a full reindex. It also means the index is only as healthy as the drive it lives on, and it disappears the moment you eject.

Cause one: the drive is formatted exFAT or FAT32

This is the one that catches most people, and it is not a fault. Spotlight does not index exFAT or FAT32 volumes. Those formats have no support for the extended attributes Spotlight relies on, so macOS quietly skips them.

Drives sold preformatted for use with both Mac and Windows are almost always exFAT, and so are most camera cards. If you bought the drive off a shelf and never reformatted it, this is the likeliest answer.

To check, select the drive in Finder and press Command-I. The Format line tells you. If it says ExFAT, Spotlight was never going to index it, and no amount of rebuilding will change that. Reformatting to APFS or Mac OS Extended fixes indexing, but it erases the drive, so it is only an option for a disk you are willing to wipe and refill.

Cause two: the volume is in Spotlight's privacy list

System Settings has a list of locations Spotlight is told to ignore, and drives end up on it more often than you would expect. Sometimes deliberately, years ago. Sometimes because an installer or a backup tool added it.

Open System Settings, go to Spotlight, then Search Privacy. If the drive is listed, select it and remove it. Indexing starts again on its own, and a large drive can take a long while to finish.

Cause three: the index on that drive is damaged

An index can be corrupted by an unclean eject, a power cut mid write, or a drive that is starting to fail. Symptoms are partial rather than total: some files are found, newer ones are not, and results feel stale.

Adding the drive to Search Privacy and then removing it forces macOS to throw the index away and build a fresh one. It is the same fix as cause two, used deliberately.

The part none of this solves

Every fix above shares an assumption: the drive is plugged in. Get the index healthy and search works beautifully, right up until you eject. Then the index leaves with the drive, and the files become unfindable again, because the thing that knew about them is sitting in a drawer.

For one working drive that is fine. For a shelf of archive disks it is the whole problem. You end up plugging drives in one at a time to answer a question you should be able to ask once.

Keeping a catalog on the Mac instead

GetFerret takes a different approach. It reads a drive once and stores the catalog on your Mac, not on the drive. Names, sizes, dates, folder structure and previews stay searchable after you eject, so you can find out which disk holds a file before you go looking for it.

It also indexes exFAT drives and camera cards that Spotlight refuses outright, because it does not depend on the volume supporting extended attributes.

It is not a replacement for Spotlight on your startup disk. Spotlight is better at searching inside documents you are working on right now. It is a replacement for plugging in five drives to find out which one has the file.