External hard drive not indexed by Spolight on Mac OS X Mountain Lion

Solution 1:

From the Terminal application type the following:

mdutil -s /Volumes/<your_disk_name>/

If indexing is disabled you will get something like that:

/Volumes/<your_disk_name>:
Indexing disabled. 

You can turn it on by typing (it will request your password):

sudo mdutil -i on /Volumes/<your_disk_name>/

Now erase all the existing entries in the index for that drive (if any):

mdutil -E /Volumes/<your_disk_name>/

Check that indexing has been enabled:

mdutil -s /Volumes/<your_disk_name>/

If indexing is enabled you will get something like that:

/Volumes/<your_disk_name>:
Indexing enabled. 

Now just reboot your system or wait some minutes until Finder begins the indexing.

Solution 2:

Esmitex, kindly try the following steps:

1. From the Apple () menu, choose System Preferences.
2. Click Spotlight.
3. Click the Privacy tab.
4. Drag a folder or an entire volume (your hard drive) to the list.
5. If prompted for confirmation, click OK.
6. Remove the item or volume you just added to the list by clicking it and then clicking the minus ("-") button.
7. Close Spotlight preferences.
8. Spotlight will re-index the contents of the folder or volume.

If the steps mentioned above does not work, try downloading this supplemental update for Mountain Lion and repeat the steps above.

http://support.apple.com/kb/DL1600

Hope this helps...