Configuring Failure Domains

A failure domain is a set of services which can fail in a correlated manner. Due to correlated failures it is very critical to scatter data replicas across different failure domains for data availability. Failure domain examples include:

• A single disk (the smallest possible failure domain). For this reason, Virtuozzo Storage never places more than 1 data replica per disk or chunk server (CS).
• A single host running multiple CS services. When such a host fails (e.g., due to a power outage or network disconnect), all CS services on it become unavailable at once. For this reason, Virtuozzo Storage is configured by default to make sure that a single host never stores more than 1 chunk replica (see Defining Failure Domains below).
• Larger-scale multi-rack cluster setups introduce additional points of failure like per-rack switches or per-rack power units. In this case, it is important to configure Virtuozzo Storage to store data replicas across such failure domains to prevent data unavailability on massive correlated failures of a single domain.