How macOS actually works

Time Machine and file search

Updated 2026-08-05 · 5 min read

A customer's scan reached 34,574,514 files and was still climbing after fifteen hours. The cause was one attached drive.

What is actually on a Time Machine drive

Not "your backups" as one copy. A complete snapshot of the Mac for every backup ever taken. Hundreds of them, each containing a full directory tree.

The storage is efficient — hard links historically, APFS snapshots since macOS 11 — so the disk usage is far smaller than the apparent contents. But a program *walking* the volume does not see that efficiency. It sees hundreds of complete copies of your Mac, and it walks every one.

What that does to a scan

A real case, from a customer with six external drives:

• 34,574,514 files scanned, still climbing
• fifteen hours elapsed, the computer running continuously
• 3.81 GB of memory in use
• progress reported as 55.8%, and falling as the estimated total grew

The scan was not stuck. It was working perfectly on a problem with no end.

Arithmetic makes it obvious in hindsight: a normal Mac indexes at roughly 42,000 files per second, so even 62 million files should take about 25 minutes. Fifteen hours means something was multiplying the work, and only one thing on that disk could.

Why tools miss it

Spotlight refuses Time Machine volumes outright. Third-party tools have to implement the exclusion themselves, and the layout changed: Backups.backupdb on HFS+, and since macOS 11 a set of <timestamp>.backup directories on APFS.

Excluding only the old layout looks correct in code and in testing, and fails on every modern Mac. That is precisely the bug in the case above — ours, found and fixed after the customer's fifteen hours.

How to tell this is your problem

• an indexer running for hours on a Mac that is not enormous
• a progress percentage that goes down, or a total that keeps growing
• a Time Machine drive attached
• memory use climbing steadily

What to do

Exclude the Time Machine volume from whatever is indexing it. A good tool does this without being asked, and says so rather than reporting the drive as "not indexed yet", which reads as a failure.

Do not turn off Time Machine. The backup is worth vastly more than the search index.

Common questions

Why is my file indexer scanning millions of files?

Usually an attached Time Machine drive. It holds a complete copy of your Mac for every backup taken, so a scan walks hundreds of full copies.

Does Spotlight index Time Machine drives?

No, it refuses them, for exactly this reason. Third-party tools have to implement the same exclusion themselves.

Should I disconnect my Time Machine drive to fix search?

No. Exclude the volume in your search tool's settings, or use a tool that skips Time Machine destinations automatically. Keep the backups.