Passive Servers and Failover Support
One new feature offered in SQL Server 2005 is enhanced failover support. For example, two or more servers running SQL Server can be configured so that if one server fails, its processing will be picked-up, recovered, and continued by the other server. SQL Server 2005 offers three types of failover support:
| • | Database mirroring is a new SQL Server 2005 technology for increasing database availability. It transfers transaction log records directly from one server to another and can quickly fail over to the standby server. |
| • | Failover clustering is a process where the operating system and SQL Server 2005 work together to provide availability in the event of an application failure, hardware failure, or operating-system error. Failover clustering provides hardware redundancy through a configuration in which critical resources are transferred automatically from a failing machine to an equally configured server to help ensure continuity of service. |
| • | Backup log shipping increases the availability of a SQL Server by automatically copying and restoring the database's transaction logs to another database on a standby server. Because the standby database receives all changes to the original database, it is an exact duplicate of the original database—out of date only by the delay in the copy-and-load process. You then have the ability to make the standby server a new primary server if the original primary server becomes unavailable. When the original primary server becomes available again, you can make it a new standby server—effectively reversing the server roles. |
When doing failover support, a server is designated as the passive server. The purpose of the passive server is to absorb the data and information held in another server that fails. A passive server does not need a license if the number of processors in the passive server is equal to or less than the number of processors in the active server. The passive server can take the duties of the active server for 30 days. Afterwards, it must be licensed accordingly.
Database mirroring and failover clustering are available for SQL Server 2005 Standard Edition and SQL Server 2005 Enterprise Edition. Backup log shipping is available in SQL Server 2005 Workgroup Edition, SQL Server 2005 Standard Edition, and SQL Server 2005 Enterprise Edition.
The following figures show a passive server that does not require a license, and another one that does require the license.
Figure 1. The passive server does not require a license because no queries are being executed against it.
Figure 2. The passive server requires a license because queries are being run against snapshot reporting.
Return to How to Buy page.
