Random crashing/kicking

Back story: Me and a small group of friends are playing an FTB Mindcrack server which started out on my local machine before we set up a dedicated server running a Xeon 2.8ghz processor and 4GB of ECC ram. I never had a single issue running and playing on the server on my local machine until the server started getting large enough I was starting to suffer performance loss so we switched to the server.

Important info:
2.8ghz Xeon
4GB ecc ram
Running MineOS on ESX with 3/4GB ram allocated
Minecraft version: FTB Mindcrack pack with MCPC legacy with World edit and dynmap plugins

Problem: Ever since the mindcrack got going on the new server computer there have been numerous crashes and even just being kicked while the server seems to do a ram dump and starts back up. Not to mention the lag spikes are shocking. I have just watched a lag spike closely on the web-ui and noticed the load averages shoot up and the free ram drop from 1GB to less than 100MB and the server itself idles around 1.6GB out of 2.5GB allocated.

What can I do to try and diagnose what’s happening and sort out these lag spikes/kicking and crashes?

When your server is experiencing spikes or otherwise feels sluggish, check a few areas:

  1. top, for the load averages. Load averages tell you how much CPU work your system is trying to do and is compared to the amount of cores you have in your system. If you have a 4.5 load average and 4 cores, you’re CPU bottlenecked, likewise 1.5 to a single-core…etc.

  2. There’s also iotop and alternatives I haven’t tried, like sar. These will tell you if you’re HDD bottlenecked.

  3. FTB is notorious for many plugins, many of which can be susceptible to leaks. What was the system uptime compared to when the slowness kicked in?

  4. Do the logs report anything on crashes?