SQL 2005 Data mirroring (Synchronous) with Log shipping sounds to be a good HA solution, when compared to the clustering. Data mirroring is for HA and Log shipping is for DR (Disaster Recovery).

While we test our application in clustering environment, we found that the failover took around 4 minutes of time. From the technical people perspective, this 4 minutes time is not acceptable and it is not HA and they added that the failover should not exceed 20 seconds of time. Also the clustering requires the shared disk. There are various types of shared disks like SAN, NAS available in the market, which are very expensive. Then we dropped the clustering solution and went for Data Mirroring (Synchronous) with Log shipping solution.

In SQL 2005 Data Mirroring (Synchronous), the transaction gets committed both in the primary database server and in the secondary database server simultaneously. Hence on failure of the primary database server, our application will to connect to the secondary database server immediately, with out any manual intervention, since both primary database and secondary database will be in sync at any time. This failover happened around 20 seconds of time.