I have my database installed on a 8 HDDs (2.5", 15k SAS) server. My website is working well now, but sometime when I make a hard delete or some hard action related to my post table (16m records now), my website become lag. Because XF doesn't support Mysql Replication, I'm thinking about upgrade my server or move to Mysql Cluster. I think a server with 8 SSD Drives or 20 SAS Drives is much better. What do you think?