I'm trying to get my head around these technologies (clusters, database mirroring, replication and AlwaysOn) at a high level. Please confirm if my understanding is correct and fill in the holes where needed.
First, a Widows Server failover cluster is two or more server nodes sharing a common SAN. The two or more servers appear as one server on the network. If a physical box fails another node is there to prevent any interruption of service.
A SQL Server cluster is an installed instance of SQL server on each cluster node, appearing as one instance of SQL Server on the network. The database(s) filegroups are located on the SAN. This arrangement provides can provide continuous service if a SQL server goes down but does not offer production if the SAN fails.
So far, so good?
Database mirroring is a SQL server technology which maintains a copy of a database on a different SQL Server instance. If the storage hosting a database goes down, mirroring is the technology that allows for (in some configurations) uninterrupted service. It seems as if, if mirroring is implemented that service could be protected if the server goes down if the mirrored SQL instance is on another host. So is SQL Server mirroring a less sophisticated (poor man's) SQL Server cluster?
From my reading, the implication is that replication is a "better" technology than mirroring (there certainly are more options). But if this is true, why? What protections does replication offer that mirroring doesn't? (Mirroring seems to offer very high reliability.)
Is AlwaysOn technology only installed on Windows Server clusters. Is it the brand name for SQL Server clusters? Or does it offer some protections or features beyond a SQL Server Cluster?
I know books are written on this. Really appreicate a high level clarification to help me understand what I'm reading.
Thanks.
Karl Thompson