Database Reference
In-Depth Information
You can monitor SQL Server cluster instances similar to non-clustered ones. You should use a virtual SQL Server
instance name, which ensures that the monitoring target always represents an active SQL Server instance, regardless
of the cluster node where it is currently running.
you can read more about sQl server Failover Clustering at: http://technet.microsoft.com/en-us/
library/hh270278.aspx
Note
Database Mirroring
The implementation of a Windows Failover Cluster was a very complex and expensive process until the release of
Windows Server 2008. Formerly, it required the purchase of expensive hardware from the Windows Cluster Hardware
Compatibility List, and it necessitated a complex set up and configuration process. This made the implementation of
a SQL Server Failover Cluster very challenging, especially for small businesses that did not have a large enough budget
nor the IT skills to implement it properly.
Database Mirroring was introduced in SQL Server 2005, and it dramatically simplified the implementation of
high availability solutions. Moreover, it removed the “storage is the single point of failure” limitation and supported
automatic failover as an option.
There are always two servers involved in database mirroring: the principal server and the mirror server. Clients
connect to the principal server while reading or modifying data. The principal server constantly sends log records
over the network to the mirror server, which saves (hardens) those records in a transaction log and replays them,
re-applying the changes to the data files.
Database Mirroring works on the database level. Every database can participate in a single mirroring session—it
is impossible to mirror the database to the multiple servers. Each SQL Server instance, however, can host multiple
mirrored databases.
Database Mirroring can either be synchronous or asynchronous. Synchronous mirroring guarantees no data
loss for committed transactions as long as mirroring is up to date and both servers can communicate with each other.
In synchronous mode, the principal server does not send an acknowledgement that a transaction is committed to
the client until the mirror hardens a commit log record in its transaction log. Figure 31-5 illustrates the step-by-step
commit process in this mode.
 
 
Search WWH ::




Custom Search