I'm using a fresh install of 10.8 Mountain Lion on a 2011 MBP. It's a work laptop with many ASCII files containing numerical data (floating point numbers), with varying file extensions. Some of the files are multi-gig, some are only a few hundred K, and there are tens of thousands of them. Roughly 500G of numerical data. I can disable spotlight from indexing certain subdirectories of my home directory on the local drive. However, when using Time Machine to backup, I seem to be entirely unable to prevent spotlight from attemping to fully index the external drive (Time Machine volume). I actually let spotlight run for over 36 hours this weekend in a futile attempt for it to finish indexing the TM volume. The /.Spotlight-V100 index on the external drive is roughly 100G and continuously written and overwritten. /var/log/system.log had various "Merging failed" messages for temp spotlight files. I deleted the index, let spotlight run again overnight, but it did not finish indexing. "sudo fs_usage -f filesys mds mdworker mdimport mdworker32 | grep open" showed spotlight slowly chugging through the thousands of numerical files. I believe the problem is related to this old report from someone who noticed a leopard -> snow leopard change: http://hintsforums.macworld.com/showthread.php?t=106703 http://forums.cnet.com/7723-6126_102-366184/snow-leopard-10-6-spotlight-indexing-and-disk-usage/ However, I don't see an easy solution. In ML, if you drag the TM volume to the spotlight privacy list it gives you a message about how you can't disable indexing of TM volumes because it's essential for TM. I have not yet tried to manually put in some kind of .metadata_never_index file in the relevant TM volume directories (I am not sure if that will do anything, or perhaps break TM backups), but that's one possible next step. Anyone have ideas on how I can have my TM backups work but the spotlight indexing of all these data files (their subdirectories) disabled? I'm not specifically TRYING to back up those data files with TM (they're duplicated elsewhere), they're just on the same machine as a bunch of other stuff I need backed up via TM. Apple has a disaster on their hands for anyone trying to backup a machine which also has large data sets.