HP Storage Mirroring V5.1 Software - Manual (Page 112)

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Failover for High
Availability
Failover is the process in which a target stands in for a failed source. As a result, user and application
requests that are directed to the failed source are routed to the target.
Storage Mirroring monitors the source status by tracking network requests and responses exchanged
between the source and target. When a monitored source misses a user-defined number of requests,
Storage Mirroring assumes that the machine has failed. Storage Mirroring then prompts the network
administrator to initiate failover, or, if configured, it occurs automatically.
The failover target assumes the network identity of the failed source. When the target assumes the
identity of the source, user and application requests destined for the source machine or its IP
address(es) are routed to the target.
When partnered with the Storage Mirroring data replication capabilities, failover routes user and
application requests with minimal disruption and little or no data loss. In some cases, failover may
be used without data replication to ensure high availability on a machine that only provides
processing services, such as a web server.
Failover can be configured to stand in for one or more IP addresses associated with different NICs on
the source. Each IP address can be added to a specific target NIC making NIC configuration very
flexible. For example, a single NIC on the source may have one or more IP addresses assigned to it.
If that source or the NIC fails, all traffic from the source is directed to the target. If there are multiple
NICs on the source, the target can assume the traffic from all of the addresses. Additional NICs on
the target increase flexibility and control. Secondary target NICs can assume the traffic from a failed
source NIC while normal target traffic can continue to use the primary target NIC.