EMC - VNX2 - How DataMover Failover

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The failover process consists of a Primary Data Mover failing and a designated Standby Data Mover being activated as a spare to take the Primary’s place. If a Primary Data Mover becomes unavailable, the Standby assumes the MAC and IP addresses of the Primary Data Mover and provides seamless and uninterrupted access to its file systems.
Creating a Standby Data Mover ensures continuous access to file systems. When a Primary Data Mover fails over to a Standby, the Standby Data Mover assumes the identity and functions of the failed Data Mover.
To act as a Standby server, a Data Mover must first be configured as a Standby for one or more Primary Data Movers. For example, you can have one Standby Data Mover acting as a Standby for three other active Data Movers. If one of the Primary Data Movers fails over, the Standby Data Mover assumes the IP and MAC addresses and functions of the failed Data Mover. The former Standby is now a Primary and is no longer available in a Standby capacity.
The Standby Data Mover must have the same type of network interface cards (NICs) as the Data Mover with which it is associated. Any FTP, archive, or Network Data Management Protocol (NDMP) sessions that are active when the failure occurs are automatically disconnected and must be manually restarted.

To detect a Data Mover failure, the Control Station monitors the various conditions of all Data Movers through the redundant internal networks that connect the Control Station to each Data Mover. If the Control Station detects a failure, it responds according to the policy type established when the Standby relationship was created. If the problem persists, and if CallHome or Email Home is configured, the Control Station calls EMC Customer Service or your service provider with a notification of the event and diagnostic information. Note: If the Control Station is not running, Data Mover failover cannot occur. When the Control Station returns to service, it will recognize the Data Mover failure and initiate the appropriate action depending on the automatic, retry, or manual failover policy

When any failover condition occurs, you can transfer functionality from the Primary to the standby Data Mover without disrupting the availability of the file system. The standby Data Mover assumes the following identities from the faulted Data Mover:

• •Network identity — IP and MAC addresses of all its NICs

• •Storage identity — File systems controlled by the faulted Data Mover

• •Service identity — Shares and exports controlled by the faulted Data Mover The Standby Data Mover assumes user file system services (if the policy is set to automatic) within a few seconds of the failure, transparently, and without requiring users to unmount and remount the file system. The definition of failover is the process of immediately routing data to an alternate data path or device to avoid interrupting services in the event of a failure. 

The impact to service is dependent on the application’s ability to handle the change gracefully. During normal operation, the VNX Control Station continually monitors the status of all Data Movers. If a Primary Data Mover fails, the Control Station detects the failure via the NAS Master Control Daemon communication over the dedicated network. It instructs the Standby Data Mover to take over as Primary while forcing the original Primary, if it is still running, into a failed state. Once failover is enacted, the Standby Data Mover becomes the Primary and resumes the entire identity of the failed Data Mover. In most cases, this process should have little, or no noticeable effect on user access to data. The Data Mover failover process works the same way in systems with two Control Stations. In the event of a Primary Control Station failure the Standby Control Station assumes the Primary role and it is responsible for the Data Mover failover. ..

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