My server is a 32 GB Ram, 2 x 6 Core 2620 --> 12 Cores - 24 Threads, Raid-10 - 4 x 1TB dedicated server. For about a month now I have had a high load issue when I get to about 500 members. I use DDoS software, blocked about 80 countries, use NGINX. Nothing seems to work and my admins cannot put a finger on it and now they are asking me to have Xenforo look at the software and give a recommendation on what to do. They think it revolves around the size of the website somehow. I am going to relay info as I am not a tech.
200-300 its at about 15-20 load at 500 it's 75 linux load
It is likely that the server needs optimising and tuning, specifically for InnoDB.
Can you provide output of any of DB scripts? U can use mysqltuner for starting. During high load, are u running out of memory or IO? You need to provide some stats, during high load and during normal load so we can help you.