September 1, 2011 at 3:50 am
Hi,
How SQL Server decides to failover ? As per my understanding when there is no heartbeat response from another node2 then node1 decides to failover. Please correct me if I am wrong. And is there any other thing that SQL Server consider to failover ?
Thanks in advance.
September 1, 2011 at 5:26 am
Failover is not just associated to the heartbeat. The Public connection is also taken into account. If the public NIC is not responding communications with Live applications will be unavailable and this will trigger a failover.
All of this is outside of SQL Server and occurs at the operating system\cluster level although there is an IsAlive check performed to the SQL Server instance. For more details regarding clusters and communications read this link
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September 2, 2011 at 1:32 am
Hi,
a clustered application is a group of resources.
All these resources are necessary to run the application (eg. SQL Server)
You'll need disk drives to store the database files, ip addresses, network names and the SQL Server services (DB engine and agent).
If one or more of these resources fail, the cluster manager tries to restart them on the original node. If it fails the whole group will be move to another cluster node and will be started there.
So, a failure of any resource will lead to a fail over.
September 2, 2011 at 5:30 am
Hi,
Yes it will look in the very first thing based on the heartbit signals then only it will take a decision to move the resources.
Regards
Raju
September 4, 2011 at 3:10 am
hoover (9/2/2011)
So, a failure of any resource will lead to a fail over.
Important to remember that failure of the dedicated heartbeat will not necessarily cause the cluster to failover as heartbeat communications would still be possible through the public network. Failure of the public network on the active node would cause immediate failover.
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"Ya can't make an omelette without breaking just a few eggs" 😉
September 4, 2011 at 4:24 am
Hi Perry, if heartbeat signal is using private network and anyhow private network goes down then how this heartbeat signal will use public network ?
Thanks in advance.
September 4, 2011 at 6:35 am
beejug1983 (9/4/2011)
Hi Perry, if heartbeat signal is using private network and anyhow private network goes down then how this heartbeat signal will use public network ?Thanks in advance.
As i pointed out cluster communications occur over the public connection. Confirm this by checking the public network properties in cluster manager and check for the allow internal cluster communications checkbox.
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"Ya can't make an omelette without breaking just a few eggs" 😉
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