SQL Server Clustering
SQL Server Clustering Consulting Services
Understanding the concept of a virtual server is a key to understanding
failover clustering. To a client or application, a virtual server is the
server name or IP address (es) used for access. The connection from the
client to the virtual server does not need to know which node within a
cluster is currently hosting the virtual server. A
clustered SQL
Server is known as a SQL Server virtual server. SQL Server 2000 is
built on top of Windows Clustering or MSCS because it is a cluster-aware
application.
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SQL Server Clustering
How SQL Server Clustering Works
From a
SQL Server perspective, the node hosting the SQL Server
resource does a looks-alive check every 5 seconds. This is a lightweight
check to see whether the service is running and may succeed even if the
instance of SQL Server is not operational. The IsAlive check is more
thorough and involves running a SELECT @@SERVERNAME Transact SQL query
against the server to determine whether the server itself is available
to respond to requests; it does not guarantee that the user databases
are up. If this query fails, the IsAlive check retries five times and
then attempts to reconnect to the instance of SQL Server. If all five
retries fail, the SQL Server resource fails. Depending on the failover
threshold configuration of the SQL Server resource, Windows
Clustering will attempt to either restart the resource on the same
node or fail over to another available node. The execution of the query
tolerates a few errors, such as licensing issues or having a paused
instance of SQL Server, but ultimately fails if its threshold is
exceeded.
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How SQL Server Clustering Works
SQL Server 2000 Failover Clustering
Perhaps the most important aspect of a successful SQL Server 2000
failover cluster installation is ensuring that the right hardware and
software are correctly deployed for the application designed to run on
the failover cluster. The hardware should be high performance, and scale
along with the specific needs of the application(s) accessing SQL
Server.
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SQL Server 2000 Failover Clustering
