I have a server of 12 cores, 2.4GHz and 64GB RAM. I have 8 shards, each is about 400GB size on the same machine. Total index is taking about 3TB space of 4TB SSD.

I am using some solr complex operations like highlighting, faceting, grouping and the query performance is very slow (few seconds to minute) 

If i increase the number of shards, does that improve performance ? Is there anyway to improve the performance without splitting the shards on multiple machines ?