Capacity Planning - The Practice of Cloud System Administration - page 367

Perform this calculation for each resource, whether or not you think you will need more
capacity. It is okay to reach the conclusion that you don't need any more network band-
width in the coming year. It is not okay to be taken by surprise and run out of network
bandwidth because you didn't consider it in your capacity planning. For shared resources,
the data from many teams will need to be combined to determine whether more capacity is
needed.
18.1.1 Current Usage
Before you can consider buying additional equipment, you need to understand what you
currentlyhaveavailableandhowmuchofityouareusing.Beforeyoucanassesswhatyou
have, you need a complete list of all the things that are required to provide the service. If
you forget something, it won't be included in your capacity planning, and you may run out
of that one thing later, and as a result be unable to grow the service as quickly as you need.
What to Track
The two most obvious things that the provider of an Internet-based service needs are some
machines to provide the service and a connection to the Internet. Some machines may be
generic machines that are later customized to perform given tasks, whereas others may
be specialized appliances. Going deeper into these items, machines have CPUs, caches,
RAM, storage, and network. Connecting to the Internet requires a local network, routers,
switches, and a connection to at least one ISP. Going deeper still, network cards, routers,
switches, cables, andstorage devices all havebandwidth limitations. Someappliances may
havehigher-endnetworkcardsthatneedspecialcablingandinterfacesonthenetworkgear.
All networked devices need IP addresses. These are all resources that need to be tracked.
Takingonestepback,alldevicesrunsomesortofoperatingsystem,andsomerunaddi-
tional software. The operating systems and software may require licenses and maintenance
contracts. Data and configuration information on the devices may need backing up to yet
moresystems.Steppingevenfartherback,machinesneedtobeinstalledinadatacenterthat
meets their power and environment needs. The number and type of racks in the datacenter,
the power and cooling capacity, and the available floor space all need to be tracked. Data-
centersmayprovideadditionalper-machineservices,suchasconsoleservice.Forcompan-
ies that have multiple datacenters and points of presence, there may be links between those
sites that also have capacity limits. These are all additional resources to track.
Outside vendors may provide some services. The contracts covering those services spe-
cify cost or capacity limits. To make sure that you have covered avery possible aspect, talk
to people in every department, and find out what they do and how it relates to the service.
For everything that relates to the services, you need to understand what the limits are, how
you can track them, and how you can measure how much of the available capacity is used.