2.5. Understanding Failure Domains¶
A failure domain is a set of services which can fail in a correlated manner. To provide high availability of data, Virtuozzo Storage spreads data replicas evenly across failure domains, according to a replica placement policy.
The following policies are available:
- Host as a failure domain (default). If a single host running multiple CS services fails (e.g., due to a power outage or network disconnect), all CS services on it become unavailable at once. To protect against data loss under this policy, Virtuozzo Storage never places more than one data replica per host. This policy is highly recommended for clusters of five nodes and more.
- Disk, the smallest possible failure domain. Under this policy, Virtuozzo Storage never places more than one data replica per disk or CS. While protecting against disk failure, this option may still result in data loss if data replicas happen to be on different disks of the same host and it fails. This policy can be used with small clusters of up to five nodes (down to a single node).