Cassandra is a highly-distributable NoSQL database with tunable consistency. What makes it highly distributable makes it also, in part, vulnerable: the whole deployment must run on synchronized clocks. In the first part of this two part series, I’ll cover how important clocks are and how bad clocks can be in virtualized systems (like Amazon EC2) today. In the next installment I’ll go over some disadvantages of off-the-shelf NTP installations and how to overcome them.