Microsoft Hotmail service is a leading provider of free, Web-based e-mail, which in January surpassed 100 million active users worldwide and continues to grow at the rate of approximately 11 million users per quarter. On a typical day, there could be as many as 350 thousand mailbox additions and 200,000 retired. That is over 550,000 change requests in a single day. Hotmail chose Microsoft Windows 2000 Server to keep pace with this applications vital need for greater performance, increased scalability, foreign language support, and shorter development cycles.

Microsoft Hotmail web-based e-mail service is one of the most widely adopted free e-mail services available on the Internet. Acquired by Microsoft in 1997, with an installed base of 9 million users, the e-mail service now comprises the largest server farm in the MSN network of Internet services Web properties. The original builders of the application created a two-tier architecture built around various UNIX systems. FreeBSD, a UNIX-like system similar to the Linux operating system, was used to run the front-end Web servers that handled login, Microsoft Outlook Express, and Web-based content delivery tasks. The current network of more than 5,000 servers is organized into about a dozen clusters; each consisting of front-end servers linked to data storage machines.

During June and July of 2000, the Hotmail site was converted from FreeBSD running Apache Web services to Windows 2000 Server running Microsoft Internet Information Services 5.0. The purpose of this technical case study is to describe how that migration was accomplished. The technical case study and the actual process of migration are broken down into three distinct stages, specifically: planning, deploying, and operating. The emphasis of this technical case study will be to describe, "How the migration was accomplished" and the factors that were key to its success.

This technical case study draws heavily from the Microsoft Hotmail migration experience. However, since the time of that migration, certain practices were further refined, and this technical case study attempts to incorporate many of the current methods of operating system deployment and migrations.

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