# Shared Storage

A traditional EMS server configured for fault tolerance relies on its state being shared by a primary and a secondary instance, one being in the active state while the other is in standby, ready to take over. The shared state relies on the server store and configuration files to be located on a shared storage such as a SAN or a NAS using NFS.

By contrast, the fault tolerance model used by EMS on OpenShift relies on OpenShift restart mechanisms. Only one EMS server instance is running and, in case of a server failure, will be restarted inside its container. In case of a failure of the container or of the corresponding cluster node, the cluster will recreate the container, possibly on a different node, and restart the EMS server there.

Within the container, the health of the EMS server is monitored by two health check probes:

- liveness
- readiness

For more information on the probes, see Health Checks: Liveness and Readiness Probes.

The server requires its state to be shared. The shared storage required by EMS on OpenShift is NFSv4.

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