High Availability - Always on Technology reduces downtime on business-critical databases with a wide range of high availability solutions. This results in data being available to customers and employees 24 hours a day, 7 days a week, while still delivering cost-effective high performance. The Always On features in SQL Server 2008 increase protection against system and hardware errors, reduce the number and recovery times of planned or unplanned downtime, and decrease conflicts caused by large numbers of users accessing the same database.
Application downtime can adversely affect business and result in lost revenue, customer dissatisfaction, and damage to credibility. Many database applications, especially enterprise business applications, require minimum system downtime. System downtime can be caused by a variety of issues such as human error, natural disaster, hardware or software failure, and application upgrade. Microsoft® SQL Server® Always On Technologies provide a full range of options to minimize downtime and maintain appropriate levels of application availability.
Symtex work with clients to understand the commercial objectives and align the technology selection, or multiple selections, to the requirements. Our expert consultants understand the intricacies and benefits behind each technology selection designing the best high availability database and application solutions for you.
Database Mirroring Database mirroring is a technology for increasing database availability. As changes are applied to the principal database they are automatically applied to the mirror. In the event of a failure on the principal server, client applications are automatically redirected to the mirror server without any changes to the application.
Log Shipping is a high-availability technology that provides a warm standby server. A back up is taken of the master server and restored on one or more secondary servers. Log shipping then applies periodic log backups to the secondary servers. While database mirroring can only have one mirror server, log shipping can have many secondary servers, which increases the level of protection. Log shipping can also take advantage of backup compression to reduce the size of the log files.
Failover Clustering is a Microsoft Windows® feature that provides protection to the entire server, not just the databases. Multiple servers, known as nodes, share a disk array so if one node fails, its services can be started on another node in the cluster. This solution prevents any data loss and provides automatic client redirection, although the failover from primary to secondary server is not as fast as database mirroring and specialized hardware is required.
Geographically dispersed failover clustering provides server-level redundancy on a certified Microsoft Geographically Dispersed Cluster Services configuration with SAN replication and a VLAN. If the site, the server node, or the disks fail, the complete redundancy of systems and disks enables the failover cluster to handle subsequent activities on another site. This configuration removes the risk of failure of a shared disk array, which would prevent a standard cluster configuration from working. Server nodes do need to be on the same the subnet.
Peer-to-peer replication enables multiple databases to be replicated with each other. Changes are allowed on any database and can be applied to other nodes in the replication topology in close to real time. Applications must be designed to connect to another node in the topology if their principal server is unavailable.
Fast Database Recovery The SQL Server 2008 Enterprise Database Engine provides fast recovery during both crash recovery and database mirroring failover. Fast recovery makes the database available during the undo phase of the recovery process, with partial availability during restore operations, database page checksums, and backup media mirroring. By supporting fast recovery, SQL Server 2008 minimizes the time taken to bring a database online, so the database is available to users sooner than if the entire recovery process had to be completed before users and applications can connect.