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SQL Server provides a high degree of functionality and performance at a low cost. It is widely supported by third-party packaged applications and by a broad range of development tools. It runs on industry-standard servers that have unmatched price performance. As a result, it is unsurprising that its use has grown as much as it has. However, the very attributes that have made it attractive have given rise to problematic patterns of growth.
- One database, one server: In many environments, administrators deploy a new server each time a database is required. When a packaged application is implemented that requires a database, a new machine is purchased and provisioned with SQL Server. When an in-house application is developed that requires a database, a new server is used. This one database/one server approach has the merit of simplicity, and the relatively low cost of SQL Server and the hardware on which it runs makes it feasible. However, as we discuss in the following section, the result is a great deal of complexity and ongoing operational expense. (In some cases, further servers are purchased to support development and test environments—one database, multiple servers!)
- Proliferation at the departmental level: Because SQL Server is relatively easy to buy and implement, it has often been purchased and deployed in an uncoordinated way at a departmental level, even in organizations that have well-organized central IT facilities. Over time, the number of servers dedicated to running SQL Server can grow to an astonishing degree, with correspondingly high ongoing costs.
- Inadequate provision of high availability: There are well-established ways to implement high availability for SQL Server databases, typically using failover clustering in active-passive server pairs. However, as we discuss in the following section, these approaches introduce significant extra cost and much complexity compared to non-clustered SQL Server. The result, in many cases, is that the threshold required to justify a highly available implementation has been quite high. Consequently, it is commonplace to find databases that in fact are important for continuing business operations but are unprotected by high availability. This is a further consequence of the relatively uncoordinated deployment of SQL Server.
Together, these creeping patterns have created what many IT managers are calling SQL sprawl: widespread, relatively uncoordinated and/or unplanned database deployments, typically in the form of many individual servers and a smaller number of active-passive server pairs clustered for high availability. Depending on the size of the organization, SQL sprawl may affect tens, or hundreds, or even thousands of servers. Regardless of the absolute numbers involved, SQL sprawl represents a waste of resources and an ongoing burden on the IT infrastructure. The next section teases out some of the costs imposed by SQL sprawl.
Low levels of utilization
The one database/one server approach to database deployment has, inevitably, produced appallingly low levels of utilization. In our experience working with customers, it is not uncommon to find most database servers running at 5–15% CPU utilization—particularly with modern server hardware. Of course, low levels of utilization imply higher-than-necessary capital costs, or, looking at it another way, low levels of utilization mean there is a large amount of stranded capacity in the environment that could be put to better use.
While low utilization levels arise in some cases because of the simplicity of deploying a new server for each database, other factors can be at work. In a typical environment, the penalty for under-provisioning a machine for SQL Server is high. This often causes a last-minute procurement of a larger and faster server as a replacement and a weekend or evening spent configuring the new machine, copying the database to it, and testing that it works properly. Figure 2 illustrates just how painful this can be. To avoid this, it is simpler to buy a large server up front, even though that inevitably produces large amounts of stranded capacity.
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