Important performance factors
Index Manager is a highly I/O and memory-intensive application. The defining factor that affects its performance is where you store the folder that contains the indexes and the location of the cache. Ideally, they should be stored on the fastest local drive your server can offer; preferably a drive with a large cache.
Since indexes are relatively small in size, storing the indexes on an SSD is the ideal solution, if budget allows.
The same goes for the cache folder - because Index Manager delivers thumbnails and previews to FotoStation and FotoWeb clients, having fast access to cached assets has a very beneficial effect on the overall performance of the system.
Tip: You can use Windows Performance counters to measure Index Manager performance on the server.