Time Machine, Spotlight Indexing, and slow performance

Recently, my Mac Mini (Mid 2010 Intel Core Duo 2 2.66MHz), upgraded from Snow Leopard Server to Lion Server, started running extremely slowly.

When I ran Activity Monitor, I noticed that the "mds" process (Spotlight) was consuming a large amount of memory (1.6 GB) and CPU usage by the mds process was spiking from 25% to 75%. From a user perspective this meant that something as simple as loading a web page in Safari ground to a halt. And forget about using iPhoto!

So, while monitoring the mds process in Activity Monitor, I dragged my system hard drive into the Privacy area of Spotlight preferences in order to shut off indexing, and determine if there was any change to mds use of my system resources. Oddly, even with the system drive removed, there was still no change to mds usage of my system resources.

Next I tried dragging my Time Machine drive (an external G-Drive, connected via FireWire) and, still, no change.

Finally, I ejected the G-Drive and, to my surprise, I saw the mds process CPU and memory usage "magically" drop.

I concluded that the index on my Time Machine backup drive was corrupted, so I ran a fresh new Time Machine backup to another available drive. Then, I turned off Time Machine, erased my external G-Drive back to factory settings, and, finally, restarted Time Machine to backup to the G-Drive.

This seems to have solved all the problems I had with the Mac Mini performing so badly: The mds process now runs at about 50MB memory and less than 1% CPU, a huge improvement.

There seems to be little information online about the relationship between Spotlight and Time Machine, so I'm posting this in case anyone else has a similar problem.