Continuity Engine Shutdown/Restart Processes

Continuity Engine Shutdown/Restart Processes

This article introduces you to the correct procedures for shutting down and restarting Neverfail Continuity Engine.
Shutdown / Restart Processes

Learning objectives

At the completion of this session you should be able to:
  1. identify the consequences of exceeding the Windows shutdown time limit.
  2. Recall the definition of a graceful shutdown.
  3. Recall the definition of the ungraceful shutdown.
  4. identify causes of an ungraceful shutdown.
  5. Recall how to restart Continuity Engine from a graceful shutdown.
  6. Recall how to restart Continuity Engine from an ungrateful shut down.
  7. Identify the role and replication state of the servers after an on graceful restart.

Neverfail Continuity Engine Shutdown/Restart Overview

Windows shutdown process consists of several activities including:
  1. Saving data files that are still open including Neverfail Continuity Engine files.
  2. Shutting down running Windows services. 
The Windows shutdown process is time limited. For most applications, including Continuity Engine, the time allocated to shutdown is sufficient. However, replicating a large Send queue to a passive server may exceed the Windows shutdown time limit.
When the time limit is exceeded, Windows will force the shutdown to complete, killing all running processes. If this occurs while Continuity Engine is still replicating a large queue of updates, the data still in the queue will be lost.
 
To avoid any potential data loss, always use the Engine Management Service or the Neverfail Advanced Client to shut down Continuity Engine before shutting down Windows. Following this process will result in what is referred to as a clean or graceful shutdown. Continuity Engine shutdown process is based on the completion of replication rather than arbitrary time limits. The actual time taken depends on the amount of replication traffic and the amount of available channel bandwidth. Performing a graceful shutdown from the EMS or Advanced Management Client stops all Continuity Engine services after completing replication on the active and passive servers. 

Ungraceful shutdown

If you do not shutdown Neverfail Continuity Engine before you shutdown Windows, the shutdown is unclean or ungraceful. An ungraceful shutdown also results from a critical failure of the server, such as a power outage or hardware crash. 

Restart from a graceful shutdown

After a graceful shutdown and subsequent server reboot, Neverfail Continuity Engine automatically restarts. On the active server, this process also restarts your protected applications. If a server has not been rebooted, you must manually restart Continuity Engine on that server. After Continuity Engine services are running, it restarts the protected applications on the active server. 

Restart from an ungraceful shut down

The Primary, Secondary, and, if installed, Tertiary servers, return from the ungrateful shutdown in a passive role and consequently do not replicate any data or provide any service to client applications. This is by design as a result of the ungraceful shutdown. You can find more information on how to recover from all servers being passive in the Neverfail knowledge base. 

Wrap Up

This article discussed details about how to properly shutdown and restart servers protected by Neverfail Continuity Engine. These key points were addressed:
  1. Windows shutdown.
  2. Continuity Engine shut down.
  3. Continuity Engine restart.
  4. The Continuity Engine shut down process can be characterized as graceful or ungraceful. The graceful shutdown results in no data loss, and ungraceful shutdown may result in data loss. After a graceful shutdown and subsequent reboot, Continuity Engine restarts automatically. After an ungrateful shutdown the server restarts in the passive role.

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