Microsoft Pushes SQL Server Closer To Continuous AvailabilityMicrosoft Pushes SQL Server Closer To Continuous Availability

Microsoft Can Check another item off its "to do" list in pursuing parity with database competitors. And administrators who manage Microsoft's SQL Server databases may have a slightly shorter worry list when it comes to database downtime.

Microsoft last week added data mirroring to SQL Server 2005, pushing its database onto the same high-availability playing field as Oracle and IBM DB2.

Data mirroring refers to a database's ability to generate an up-to-the-second copy of itself that can take over almost immediately if the primary database should fail. Oracle and IBM offer data mirroring as an option for their databases. Microsoft began providing the capability last week as part of Service Pack 1 for SQL Server 2005, the most up-to-date release of its database.

SQL Server 2005 already included the ability to take snapshots for reconstructing a database at a previous point in time. But data mirroring, which was to have been included in SQL Server 2005, was delayed for more testing. Mirroring comes closer to the "continuous availability" goal set by Microsoft senior VP Paul Flessner in a speech earlier this month. With mirroring, two database servers are linked, each creating the same log of events from a stream of transactions.

Microsoft's closer ties with SAP also were evident with this week's server pack release, which includes Reporting Services that work better with SAP's NetWeaver Business Intelligence, the data storehouse for SAP applications. Microsoft also will offer SAP NetWeaver-ready versions of its own business intelligence tool and a tool for querying the SAP Business Warehouse.

But it's the database mirroring that moves SQL Server the furthest. It puts it past "warm failover" capabilities, in which a database problem might result in a few minutes of downtime, to "hot failover," in which an outage remains nearly imperceptible to users. That might seem like an incremental benefit, but for DBAs, those minutes of downtime can be very long indeed.