# Shared State

A pair of fault-tolerant servers can have access to shared state, which consists of information about clients and persistent messages.

Note: You cannot use more than two servers in a fault-tolerant configuration.

This information enables the standby server to properly assume responsibility for those clients and messages. The following image illustrates a fault-tolerant configuration of EMS.

## Locking

To prevent the standby server from assuming the role of the active server, the active server locks the shared state during normal operation. If the active server fails, the lock is released, and the standby server can obtain the lock and become active.

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