A configuration management database (CMDB) is one or more databases used as a means for information technology (IT) managers to plan and organize every aspect of an organization's IT environment. Pretty much anything that comprises the IT workings of an organization can go into a CMDB, where each entry into the database becomes what's called a configuration item (CI). This includes not only computer hardware and software inventory and control, but also methods of operation, specific incidents and changes to the IT environment, even people.
The contents of a particular CMDB may vary by department or service. The CIs for an organization are collected into a CMDB, which becomes a central information repository for tracking them and their relationships with one another. With the help of a good CMDB implementation, an organization can make more informed decisions on IT planning, management, and necessary spending for maintaining the IT infrastructure.
The idea behind the configuration management database came about from the workings of the Central Computer and Telecommunications Agency, which eventually became the Office of Government Commerce, a government agency in the United Kingdom (UK). The group maintains and publishes a series of books that describe what's known as the Information Technology Infrastructure Library (ITIL®). Part of the ITIL® involved the recommended use of databases for managing the elements of an IT environment and how they're configured.
As the ITIL® continued to garner popularity beyond UK government agencies and contracts, however, the configuration management database concept became somewhat confusing, and a bit of controversy emerged. Numerous companies raced to create actual database applications that were marketed as a single source for simplifying the management of IT departments. By the time version three of the ITIL® emerged, the idea behind the CMDB fell under a section that described a more general configuration management system (CMS) in order to better describe the idea behind the use of a CMDB. Under the new clarification, a CMS may contain one or more possible CMDBs.
Further developing the notion of the configuration management database, the idea was taken on by the Distributed Management Task Force (DMTF®), a coalition of technology industry companies. By approaching the CMDB as more of a federation of databases, using the CMS notion described in the new ITIL®, the concept proposes any number of databases, called management data repositories (MDR), and a means by which they communicate and share configuration items with one another. The DMTF® standard helps companies who wish to continue developing databases for use as MDRs to do so in a way that will work with MDRs created by others.
In essence, at the top of a hierarchy is the the primary configuration management database, which can be viewed as something of a meta-database. It doesn't need to contain all of the details regarding a particular IT environment, instead allowing other trusted sources to maintain that information. The various CMDBs of an organization then share the key data up to the primary CMDB that is then used for general decision making. Departmentalizing the CMDBs in this manner allows for better clarification and easier control of information about the entire IT environment altogether.