# Crash-Recovery System Model Characteristics

This is a model that is useful to describe systems that have nodes that can crash and recover later on.

1. The system is a set of processes $\Pi = \{ p_1, \ldots p_n\}$.
2. processes communicate by sending messages using TCP connections.
3. process has a persistent storage.
4. processes have two states: up and down.
5. process may crash and recover indefinitely many times.

Reference: ZooKeeper’s atomic broadcast protocol: Theory and practice, Andr´e Medeiros, http://www.tcs.hut.fi/Studies/T-79.5001/reports/2012-deSouzaMedeiros.pdf