I am using Lucene.Net API and building an desktop search windows application.

The indexing is very very slow, it takes about 20 minutes to index 10 GB data. i have to index all the files and search for specific text in the files.
I tried RAM indexing, no improvement in speed. Tried multi threading for indexing, no improvement. Tried changing mergefactor values, still no improvement.

Please suggest me a better design to improve this.