Capacity Planning - The Practice of Cloud System Administration - page 368

How Much Do You Have
There is no substitute for a good up-to-date inventory database for keeping track of your
assets. The inventory database should be kept up-to-date by making it a core component in
the ordering, provisioning, and decommissioning processes. An up-to-date inventory sys-
tem givesyouthedata youneedtofindouthowmuchofeach resource youhave.Itshould
also be used to track the software license and maintenance contract inventory, and the con-
tracted amount of resources that are available from third parties.
Usingalimitednumberofstandardmachineconfigurationsandhavingasetofstandard
appliances, storage systems, routers, and switches makes it easier to map the number of
devices to the lower-level resources, such as CPU and RAM, that they provide.
How Much Are You Using Now
Identify the limiting resources for each service. Your monitoring system is likely already
collecting resource use data for CPU, RAM, storage, and bandwidth. Typically it collects
this data at a higher frequency than required for capacity planning. A summarization or
statisticalsamplemaybesufficientforplanningpurposesandwillgenerallysimplifycalcu-
lations. Combining this data with the data from the inventory system will show how much
spare capacity you currently have.
Tracking everything in the inventory database and using a limited set of standard hard-
ware configurations also makes it easy to specify how much space, power, cooling, and
other datacenter resources are used per device. With all of that data entered into the invent-
ory system, you can automatically generate the datacenter utilization rate.
18.1.2 Normal Growth
The monitoring system directly provides data on current usage and current capacity. It can
also supply the normal growth rate for the preceding years. Look for any noticeable step
changes in usage, and see if these correspond to a particular event, such as the roll-out of a
new product or a special marketing drive. If the offset due to that event persists for the rest
oftheyear,calculatethechangeandsubtractitfromsubsequentdatatoavoidincludingthis
event-driven change in the normal growth calculation. Plot the data from as many years as
possible on a graph, to determine if the normal growth rate is linear or follows some other
trend.