Database Reference
In-Depth Information
How does the introduction of ESXi affect the ACID properties of a transaction? The
short answer is, it does not. The reason is that ESXi will only acknowledge a read or
write to the guest operating system after the read or write is verified by the storage
controller; if vFRC is involved, then reads are from the cache and writes go to the
storage. Once this read or write is verified, it is handed off to the guest operating system
to process, and this now becomes a Windows and SQL operation. From a physical
server or virtual server perspective, it is exactly the same when dealing with a Type 1
hypervisor such as vSphere.
Note
If you want to read Jim Gray's paper on the transaction concept, it can be
found at
http://research.microsoft.com/en-
SQL Server AlwaysOn Failover Cluster Instance
SQL Server AlwaysOn Failover Cluster Instance (FCI) is a high availability solution
for SQL Server instances. This protection is provided at the same site or across sites. It
should be noted that for SQL Server AlwaysOn FCI that span multiple sites, array-
based replication technology is required. This is the clustering solution most of us are
familiar with and that has been around for years. SQL Server AlwaysOn FCI does
leverage Windows Server Failover Clustering (WSFC) functionality. SQL Server
AlwaysOn FCI requires two instances of Windows Server to be connected to the same
backend storage. Once configured, SQL Server AlwaysOn FCI will protect against
hardware, operating system, or application issues and fail over services to the standby
SQL Server. Another popular use for SQL Server AlwaysOn FCI is for rolling upgrades
of SQL Server itself and patching of the underlying operating system. There is minimal
downtime while services transition from the failed server to the standby server. These
failovers can be automatically or manually initiated either by fault detection or
administrative interaction. With SQL Server AlwaysOn FCI, only one of the SQL
Servers can own the resource at a time, and the shared disk represents a single point of
failure.
SQL Server AlwaysOn FCI is a solid solution that provides high availability for SQL
Server databases. With Windows Server 2012 and SQL Server 2012, Microsoft has
done a nice job in hiding the complexities of configuration and have eased
administrative overhead associated with this implementation.
For a virtualized SQL Server implementation, there are valid reasons to run SQL Server
AlwaysOn FCI. There are also limitations to running SQL Server AlwaysOn FCI that
must be accounted for during the decision process as whether to virtualize these SQL
