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The Configuration Management Database (CMDB) concept of ITIL seems to
generate the most questions from readers and may stem from the relatively
small amount of information on the Web regarding it. So let’s take a few
moments to look at the seemingly arcane CMDB, and remove the needless
cloak of mysticism around it.
The CMDB is a relational database that serves as the nerve center of IT
service management. While the word ‘configuration’ makes people think it
is tracking build information, it is far greater than that. The CMDB
represents a logical model of IT. As such, it is tasked with tracking
configuration items (CI), attributes (metadata) about each and, very
importantly, their relationships to one another.
The CMDB can be all in one database or interfaced together (federated) to
preserve normalization of data, ease of collection, etc.
First off, everything is a configuration item. Hardware, software,
people, accommodations (ITIL’s term for facilities), data files,
documentation (including data records), and services are all top-level
CIs. What an organization uses, and how they use it, are based on their
needs.
For example, under hardware, maybe they need tables for each CI type to
track network devices, servers, storage devices, etc. Records, such as
those for changes, problems and incidents, also are CIs and need to be
defined based on business need. In general, you want to use a CI when
one-to-many and many-to-many relationships exist. However, risk or other
needs also may prompt you to define a class of CIs vs. simply using
attributes.
A good way to think of attributes is that they are the data fields that
make up the CI tables. As an example of CI vs. attribute, would you want
to have a field in the server CI record called ‘Operating System’ or
would you want a CI called ‘Operating System’ that then had attributes
defining each type of operating system in use? The correct answer depends
on your needs.
At the heart, we know we need to understand some basic elemental
attributes regardless of CI type such as:
documentation, etc.;
has it been retired? You want enough meaningful status values to
represent the lifecycle of the CI;
vendor ID or the internal department;
for calculating the book value;
associated with the CI. In other words, work with accounting to make sure
that the correct total purchase cost is entered. This may include
purchase price, shipping, professional services, etc.
this CI? ITIL is big on confidentiality, integrity and availability
(CIA), but you should use what makes the most sense;
groups may need to know the physical location as well as logical
locations;
attribute evolve into something unmanageable.)
For each CI type, you may add, change or delete attributes as needed, but
you want to keep the CI structure both meaningful and manageable. If the
CMDB becomes too complex to maintain, then its value plummets and people
will stop using the system out of frustration.
Database table relationships could be as follows:
a component?
component CIs make it up?
against it. This may be the same as the change record IDs but it’s listed
separately here. The reason is to show all RFCs — accepted and rejected;
allows for the Change Manager and other stakeholders to gauge historical
activity;
with?
Moving along, assembled or compound CIs are made up of n-levels of
hierarchically grouped components. A SQL Server is made up of hardware,
software and documentation. A service is made up of hardware, software,
documentation, and people. The idea is to understand how CIs are
assembled for cost, impact analysis, overall planning and so on. For
those people with a manufacturing systems background, think of an
assembled CI as being analogous to a bill of material (BOM).
One of the most important outputs of Configuration Management is the
documentation of relationship. It is critical that the CMDB be able to
relate all of the various CI types together. These relationships allow
for Change Management to do impact analysis.
If I allow this change to happen, what are the risks? Who and what are
involved? By having the relationships in the CMDB, the Change Manager can
begin to answer those questions.
The bottom line is that the CMDB is the hub system of all activity in the
world of IT Service Management. The exact tables and composition should
be driven by the needs of the business, then the services that support
those needs and finally the resources that comprise each service that IT
delivers. When people ask what a CMDB should look like, they must realize
that there is no one-size-fits-all answer. They must work to understand
what the business needs, what IT needs and then design a data model that
meets those requirements.
Note: For further reference, the ITIL Service Support volume lists
potential CI attributes in Annex 7C of Configuration Management.
