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Although virtualization can be considered a form of consolidation, in this section we ll take consolidation to mean installing multiple SQL Server instances on the one server, or moving multiple databases to the one instance. Figure 3.11 shows an example of consolidating a number of database instances onto a failover cluster. Support of NUMA hardware, the ability to install multiple instances and cap each one s memory and CPU, and the introduction of Resource Governor (covered in chapter 16) in SQL Server 2008 all contribute to the ability to effectively consolidate a large number of databases and/or database instances on the one server. Just as creating a new virtual server is simple, installing a new SQL Server instance on an existing server is also easy, as is migrating a database from one instance to another. But just because these tasks are simple doesn t mean you should perform them without thought and planning. Let s take a look at a number of important consolidation considerations for SQL Server.

Figure 3.11 Among other benefits, SQL Server consolidation centralizes administration and combats server sprawl.

In subsequent chapters we ll discuss the importance and value of collecting a number of performance monitor counters during periods of time in which performance is reported as being normal. From a consolidation perspective, having this data at hand helps you make sensible decisions on the placement of instances. For example, consolidating a number of CPU-starved servers on a single CPU core box doesn t make any sense. In contrast, consolidating servers that consume very little resources does make sense. Accurate baseline data is a crucial component in making the right choice as to which servers and/or databases should be consolidated. When examining typical usage as part of a consolidation process, take care to ensure batch processes are considered. For example, two SQL Server instances may coexist on the one server perfectly well until the end of the month, at which point they both run a large end-of-month batch process, potentially causing each process to exceed the required execution window. ADMINISTRATIVE CONSIDERATIONS Consolidation brings with it an even mix of benefits and challenges. We ve just covered the importance of consolidating complementary instances from a performance perspective. Equally important is considering a number of other administration aspects: Maintenance windows How long is each server s maintenance window, and will the combination of their maintenance windows work together on a consolidated server Disk growth Is there enough disk space (and physical disk isolation) to ensure the database growth and backup requirements can be met

Apart from the ability to affinitize CPUs and cap memory usage, choosing to install multiple instances has one distinct advantage over placing multiple databases in the one instance: each instance has its own tempdb database. Depending on the databases being consolidated, installing multiple instances allows more than one tempdb database to be available, enabling the placement of databases with heavy tempdb requirements in the appropriate instance. Let s turn our attention now to virtualization, a specialized form of consolidation.

Unlike the SQL Server instance/database consolidation techniques we ve outlined so far, virtualization occurs at a lower level by enabling a single server to be logically carved up into multiple virtual machines (VMs), or guests. Each VM shares the physical server s hardware resources but is otherwise separate with its own operating system and applications. Virtualization platforms, also known as hypervisors, are classified as either Type 1 or Type 2. Type 1 hypervisors, commonly referred to as native or bare-metal hypervisors, run directly on top of the server s hardware. VMware s ESX Server and Microsoft s Hyper-V (see figure 3.12) are recent examples of Type 1 hypervisors.