SQL Server 2008 - enhanced feature in database mirroing "log compression"
Database Mirroring - new feature from SQL Server 2005 within High Availability ranch, a software based solution for database availability.
Very important for the DBAs to keep up the database recovery model to FULL at all the times to achieve the High Availability per database level, as the feature behind SIMPLE or BULK-LOGGED does not support recovery of non-logged transactions that consists mismatch of Log Sequence Number. So this leaves monitoring the setup and performane of Database Mirroring session for the metadata with catalog or dynamic management views that are very much availble since SQL Server 2005 version. Such as:
sys.database_mirroring - for database mirroring metadata for each mirrored database
sys.database_mirroring_endpoints - for database mirroring endpoint
sys.database_mirroring_witnesses - for database mirroring metadata for each session in which a server instance is the witness
sys.dm_db_mirroring_connections - a row for each database mirroring network connection
Before you setup database mirroring ensure to check the partners and the witness, if any, must be running on the same version of SQL Server. As this is required to make sure the partners which is principal server and mirror server that are supported by Standard Edition and later versions. By default for witness you can use SQL Server Express 2005 version, verify that the mirror server has sufficient disk space for the mirror database. On a 32-bit system, database mirroring can support a maximum of about 10 databases per server instance because of the numbers of worker threads that are consumed by each database mirroring session.
The newest feature within SQL Server 2008 is Log Compression - SQLCat blog post.