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SQL Server Cluster LooksAlive and IsAlive Check


Windows Cluster Service use the “heartbeat” process to check whether each node is alive at both the OS level and SQL Server level. Heartbeat signals works on UDP.

Microsoft Windows Cluster service perform 2 health checks to perform node & resource availability check.

LooksAlive Health Check

1) LooksAlive is a quick lightweight health check

2) Run at interval of 5 Seconds

3) Does not impact performance but does not perform a thorough check

4) The check will succeed if the service appears to be running even though it might not be operational

5) If Fails calls “IsAlive” health check

6) Polling interval can be changed by adjusting LooksAlivePollInterval property of Cluster service

IsAlive Health Check

1) Run at interval of each 60 Second

2) Perform more detail check then LooksAlive

3) Run @@SERVERNAME to ensure that SQL Server is responding to queries

4) Does not ensure that all user databases are operational

5) Retired 5 times & then try to reconnect SQL Server

6) If all 5 retry fails, the SQL Server resource fails & Windows Cluster service will try to bring it online on other node as per configuration

7) Polling interval can be changed by adjusting IsAlivePollInterval property of Cluster service

Reference : Rohit Garg (http://mssqlfun.com/)

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Renaming or Changing SQL Server Cluster Instance


Renaming or Changing SQL Server cluster instance process is bit different from renaming a stand-alone instance.

Refer : Rename or Change SQL Server Standalone Default Instance http://mssqlfun.com/2014/06/30/rename-or-change-sql-server-standalone-default-instance/)

Refer : Rename or Change SQL Server Standalone Named Instance (http://mssqlfun.com/2014/07/29/rename-or-change-sql-server-standalone-named-instance/)

The name of the virtual server is always the same as the name of the SQL Network Name (the SQL Virtual Server Network Name). You can change the name of the virtual server, you cannot change the instance name like in the case of standalone named instance. You can change a virtual SQL server named SQLServerinstance1 to some other name, such as SQLServerNewinstance1, but the instance part of the name, instance1, will remain unchanged.

Rename a virtual server :-

1. Using Cluster Administrator, change the SQL Network Name or SQL Server DNS Name to the new name.

2. Take the network name resource offline. This takes the SQL Server resource and other dependent resources offline as well.

3. Bring the SQL Server resource back online.

Verify the Renaming Operation :-

1) Using @@ServerName

2) Using sys.servers

Minimize network propagation delay :-

ipconfig /flushdns

ipconfig /registerdns

nbtstat –RR

You are done ! You should ask your application teams to reconnect with new Name or if they are using IP address then no changes required.

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Reference : Rohit Garg (http://mssqlfun.com/)