Ask HN: server I/O spike

I have an app on linode and they sent me an email letting me know of a spike in disk I/o that lasted about 2 hour ad now it's back to normal.

What should I look at when diagnosing what happened?

Weird things at first glance:

1) A spike of incoming network traffic happened at 22:00 2) A spike of outgoing network traffic between 2:00 to 4:00 3)Disk I/O between 6:00 and 8:00