SQL 2005 Mirroring
During a presentation today I discussed the new mirroring functionality of SQL Server 2005 and was asked what editions it will be available in.
There are a number (quite a few) changes in terms of replication in SQL Server 2005, including peer to peer replication, http replication and other options. One of the availability options that is really nice in SQL 2005 is database mirroring - here's a quick overview.
SQL Server 2005 allows for synchronous or asynchrnous mirroring with fully automated failover. The sync/async option means you can have the transaction commit at both ends simultaneously or commit the primary site first and then the secondary site. The mirror requires no special hardware and is not restricted by distance (unlike clustering). In the case of a failure, the failover takes up to 3 seconds to take place, meaning very little perceived outage by clients.
In case of failure the mirror server assumes the role of primary server (in conjunction with the third server called a witness server). If the server that was previously the primary server comes online when the mirror has assumed the role of the primary, the server will initialize its mirror session (i.e. sync with the new primary) and the assume the role of mirror server automatically.
Administratively SQL Mirroring is easy to manage (i.e. pretty much self managing), resilient and cost effective to set up (it requires no shared hardware and works with normal server hardware).
The SQL 2005 feature comparison states that SQL Mirroring is available in Standard and Enterprise editions, making it a viable solution for smaller customers as well as for enterprise customers.