On OS X, does Time Machine need the index maintained by Spotlight? Will disabling Spotlight completely (via mdutil) affect Time Machine?

  • Are you talking about disabling Spotlight on your main drive(the one getting backed up) OR on the Time Machine drive (the one with the backup)?
    – nohillside
    Commented Jul 16, 2014 at 7:39
  • @patrix I re-enabled (after completely deleting the index) Spotlight on my main drive and now Time Machine needs a very long time to create a backup.
    – ben
    Commented Jul 16, 2014 at 10:50
  • This may also be caused by Spotlight running in parallel to Time Machine. Has the index already been completely been rebuilt before TM started?
    – nohillside
    Commented Jul 16, 2014 at 11:03
  • @patrix Yes, I let the indexer finish its work and only afterwards connected the TM drive. I did not change a lot of files after the last backup - nothing which would justify TM "preparing" the backup for two hours. (I have stopped it then and not finished the current backup yet.)
    – ben
    Commented Jul 16, 2014 at 11:20
  • Maybe a duplicate of apple.stackexchange.com/questions/236059/… Commented Sep 2, 2021 at 20:02

1 Answer 1


Yes Time Machine require a spotlight index on the backup volume. As a result, you cannot add a Time machine volume in the privacy list.

Apple explained this by stating:

If you add a Time Machine backup disk to the privacy list, you will 
continue to see messages that Spotlight is indexing your backup disk. 
This indexing is necessary for Time Machine to function properly and 
can’t be disabled. Spotlight does exclude from searches any items 
you store on your backup disk that are not part of a Time Machine

I have just tried adding my TM backup drive to the exclusion list in Catalina 10.15.4 and it was refused stating that I cannot add a Timemachine Backup to the privacy list of spotlight. - Others have tried the same in Mojave 10.14.2, in Sierra and High Sierra, with the same result.

Again others have tried doing this more ingeniously in the command line, only to find that mdworker continued to access the backups making indexes.

Oddly, though, Apple has removed its earlier article(s) about this altogether, and there is no longer any official line as to whether it’s possible.


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