TerraServer Bricks “” A High Availability Cluster Alternative

Microsoft TerraServer stores aerial, satellite, and topographic images of the earth in a SQL database available via the Internet since June 1998. It is a popular online atlas, combining twenty-two terabytes of image data from the United States Geological Survey (USGS). Initially the system demonstrated the scalability of PC hardware and software Windows and SQL Server on a single, mainframe-class processor [Barclay98]. Later, we focused on high availability by migrating to an active/passive cluster connected to an 18 terabyte Storage Area Network (SAN) provided by Compaq Computer Corporation [Barclay04]. In November 2003, we replaced the SAN cluster with a duplexed set of Y´white-box¡ PCs containing arrays of large, low-cost, Serial ATA disks which we dub TerraServer Bricks. Our goal is to operate the popular TerraServer web site with the same or higher availability than the TerraServer SAN at a fraction of the system and operations cost. This paper describes the hardware and software components of the TerraServer Bricks and our experience in configuring and operating this environment for the first year.