A Qucik guide to Server Sizing

As an infrastructure architect we generally tasks with rightly size server infrastructure to support a particular Application, so that it can provide the desired response time to the end users. Server sizing is quite a vast topic with complex mathematical models. But I will quickly go through few steps to provide a general idea.

1. First step is the work load characterisation where transactions for the particular application should be identified.

2. To find out the service demand or resource consumption by these transactions. This can be done by running a particular transaction and capturing the CPU and disk utilization.

3. Third step is to build an Analytical or Simulation model and provide service demand as an input..

Let’s take look at a very simplified example.

A website comprises of only a web server with a single CPU. The access logs records 1000 transactions in a time interval of 10 minutes and server utilization during that time was 50 %.

The service demand for that particular transaction derived as follows, during 10 minutes interval server was busy for 50 % of the time, or total CPU consumption was 5 Minutes. There were 1000 transactions during that time; service demand for that particular transaction will be 300 seconds/1000 = 0.3 Seconds.

The maximum transactions system can handle so that utilization does not go beyond 70 %, will be 0.7/0.3 = 2.3 transactions per second.

If the system needs to handle more transaction, we should consider a server upgrade.

TOGAF Framework for Infrastructure Architecture

TOGAF the framework from the open group (http://www.opengroup.org/togaf/) for the development of enterprise architecture can be easily adapted for development Infrastructure Architecture only. TOGAF provides some powerful methods. I have used it quite successfully in number of cases. I use the following phases from the Architecture development Methods (ADM).

Architecture vision
a) Identify business Goals and Business drivers
b) Review Architecture Principles
c) Define scope
d) Define constrains
e) Identify Stakeholders concerns and business requirements

The above provides inputs to the Technology Architecture or Infrastructure architecture development phase. I follow the following steps to create a broad technology / Infrastructure architecture

a) Create a baseline Technology description
b) Create an Architecture model of building blocks
c) Select the service portfolio requirement per building blocks
d) Develop the Target Technology / Infrastructure architecture
e) Gap analysis between Baseline and Target Architecture

Gap analysis provides inputs to the Opportunities & Solution Phase where projects can be identified .

The detail migration planning can be done subsequently in the Migration Planning Phase of ADM .

TOGAF can be successfully combined with the ITIL V3.0 to create the Service Strategy, Service Design and Service transitions. I will explain those in the a subsequent blog .

Of course the ADM method can be customized to individual project requirements.