You need to find out what is actually causing the IOPs.
I would advise checking:
- that your memory is not damaged
- your SWAP usage
- what your DB server is doing (check the processlist on MySQL for example)
But really you need to find out what your server is doing. Moodle is not necessarily the cause. It could be a symptom. Someone could have hacked your server and be using it for mining bitcoin, sending e-mails, or something completely unrelated.