News

Database Mirroring Not Ready for Production When SQL Server 2005 Ships

• By Scott Bekker
• September 14, 2005

Database mirroring, a high-availability feature, will be included in the RTM version of the Standard and Enterprise editions of SQL Server 2005, but customers will be required to go through extra steps to turn on the feature. Those who try to enable the feature without following the extra steps will get an error message and warning that the feature is for evaluation purposes only.

"It was a very hard decision on our side," said Tom Rizzo, director of SQL Server product management. "I don't think we've done it before in an RTM product."

Database mirroring is a new SQL Server 2005 technology for increasing database availability. Building on the log shipping that was available in the Enterprise Edition of SQL Server 2000, database mirroring transfers transaction log records from one server to another and allows quick failover from one server to another. Client applications can also be coded to automatically redirect connections to the standby server.

Rizzo said that the feature is complete and an army of test machines have beaten on database mirroring. But he said only five or six beta customers have put the feature into production, and Microsoft is uncomfortable with fully releasing a feature that has so few production deployments.

"We've got to make sure it's 100 percent rock solid. You don't want a high-availability feature that works in 99 percent of cases and not in 1 percent. I like to think of database mirroring on an extended test cycle -- as having extra bake time," Rizzo said.

In a letter to customers on Wednesday disclosing the decision, Microsoft senior vice president for server applications Paul Flessner wrote, "We are committed to making it generally available in the first half of 2006. We will continue to field-test the feature with customers and will release it for general use as soon as you tell us it is ready."

Flessner's letter also reiterated Microsoft's commitment to the Nov. 7 launch date for the database and announced the release of the September Community Technology Preview of SQL Server 2005.

Flessner also revealed that Microsoft is working on a scaled-down version of the SQL Server 2005 Management Studio for SQL Server 2005 Express Edition. "We also heard from many of you that you wanted a more seamless management experience across all SQL Server 2005 editions," Flessner wrote. "We believe this will provide you with the ability to more efficiently manage SQL Server 2005 Express Edition with increased automation and lower complexity."

Microsoft hopes to deliver the management tool for the Express Edition in the first half of 2006.

According to Flessner, more than 300,000 customers downloaded or requested CDs for the previous SQL Server CTP. He said more than 30 Microsoft customers have SQL Server 2005 running in production. At Microsoft, nearly 100 business-critical applications are running SQL Server 2005, with some of those applications running on pre-release code of SQL Server 2005 for more than a year.

Editor's Note: This story has been updated to correct the status of database mirroring in SQL Server 2005 and to add quotes and context.