On any Mac, you can experience odd slowdowns when copying or
acting on a large number of files, such as duplicating a folder
with many items in it, cloning a drive, or testing drive
performance. That's because Spotlight never sleeps. It's constantly
looking for modified or new files to index.
Spotlight's polling can have a significant performance toll. For
example, cloning speed might be half the rate you expect or even
lower. But you can tell Spotlight to keep its hands off while
performing operations that it might otherwise slow down. The secret
is the Spotlight preference pane's Privacy view (System Preferences
item into the Privacy view to add it, or click the + to select a
folder or volume.
Apple uses the term privacy to indicate you don't want items
indexed that are shown in the volumes or folders list in that view.
But it's really a don't index me list.
You can use the Privacy list in a lot of ways:
- Add external volumes that contain backups, like networked Time
Machine volumes or local clones. These don't need to be indexed.
(Volumes that are entirely devoted to Time Machine are already
excluded, but don't show up in the list.)
- When creating or updating a clone, drag its volume icon to the
list before starting. You can remove it later, but you likely don't
need the clone indexed within the current startup volume's
- Create or add folders that commonly hold large numbers of
temporary files or are used for rapid reading and writing of data
that doesn't need to be indexed. I discovered in using the Blackmagic Disk Speed Test, a free app for
determining drive performance, that placing its test file in a
Spotlight-indexed folder dramatically reduced tested throughput
compared to a folder excluded from Spotlight.
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