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Updated: January 1, 2003

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

A rolling upgrade offers multiple benefits and can be an alternative for any mission-critical system that requires high availability.

Consider two examples: Jack and Jill. Jack runs a mission-critical database application on a stand-alone Windows Server 2003based server. He regularly applies Windows Server 2003 operating system service packs (every quarter), upgrades his application once a year and performs a maintenance hardware upgrade once a year as well. From past experience, he can tell that the service pack installation takes on average of 60 minutes. An application upgrade generally takes four hours. Hardware upgrades take anywhere from 30 minutes to four hours. He can also testify that once a year, something goes wrong and an upgrade takes four times as long as planned. Total downtime per year of this system averages:

4 x 60 + 240 + 240 + 240 = 16 hours, which equals 99.8 percent uptime.

Jill runs a mission critical e-mail application on a two-node cluster. She applies the same rules as Jack, but instead of upgrading both nodes at once, she performs rolling upgrades. She measured that it takes five minutes on average to move this application from one node to another; thus, the downtime associated with each upgrade is limited to five minutes. Total downtime per year for his system averages:

4 x 5 + 5 + 5 = 30 minutes, which equals 99.99 percent uptime.

Rolling upgrades are advantageous in that they:

  • Minimize downtime. Rolling upgrades minimize downtime associated with software or hardware upgrades.

  • Minimize risk. Rolling upgrades minimize the risk of losing the service in case the upgrade fails. When an upgrade of one node fails, the other node can still provide the service, giving the system administrator the choice to repair or replace a failed node without incurring any additional downtime.

  • Increase flexibility. The nearly negligible system downtime caused by a rolling upgrade means that administrators could decide to perform a rolling upgrade during a working day instead of performing it late at night or on weekends.

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