High Availablity Solutions
Clustering is a hardware-based solution that relies on high performance fiber optic connections to a fully-redundant SAN storage solution. 4Gb infrastructure with dual fiber HBAs actually increases performance beyond local disks. Failover happens within seconds for the typical database, however extremely large databases will increase the necessary time. Two servers in an active-passive configuration share the same storage, with the SQL instance failing to the passive server in the case of failure. Transactions seamlessly move to the active server so that no changes to the database are lost. MaximumASP includes the SQL Support package for clustered solutions.
This process copies live transactions to a secondary server with automatic failover in the event of primary server failure. There is a performance loss with mirroring, as every transaction effectively has to be written twice, but since it does not require the same level of additional hardware and infrastructure, it is a more affordable High Availability solution. Mirroring is configured at the database level, so the customer must notify the SQL team when new databases or users are added, so that they can be included. Also, .NET is required to fully utilize this solution as a back-end to a website.
Log Shipping is the process of backing up a production database transaction log, then copying the backup to a second server. The backup is then restored on the second server and placed in a recovering state, typically every 15 minutes. A DNS alias is created for the customer to connect to the production SQL Server, and in the event of a failure is pointed to the standby server, which is placed into an active state. In this scenario customers must contact MaximumASP if they add databases or users. A failover takes about 15 minutes to perform, and is not automatic. This is a disaster-only solution.