1. Do you have sufficient hardware? – How may load generators are required for the entire load test?  Refer to this document from HP Support, “Is resource (cpu and memory) footprint information available to help in estimating the load generators required for load testing with LoadRunner?” for estimating the load generators required by multiplying the observations with the total number of virtual users generated in the test.   In addition to the processor utilization recommended in the document, do watch the memory and network consumption of the load generators.   The network interface card (NIC) can become a bottleneck for load generation.  A 1GB NIC will definitely generate and receive more load than a 100MB NIC.  Therefore, do a check on the machines assuming the load generator roles and make appropriate measures to prevent the NIC in becoming the bottleneck.   With the above, you will get a rough gauge of the required resource for your test.
2. Do you need spare hardware? – Do cater some spare machines if additional load generators are required, such as an additional of 5 load generators.  This is to stand by in the event of increasd virtual users and machine malfunction.
3. Remember that it’s a team effort! – Can you secure human resources for the load test?  You will need the web, application and database server teams to be around to observe the system behavior during the test or to assist in any reboot or refresh activities for the system.  Network and firewall/security team may be required to ensure that connectivity is allowed for the load test.    Therefore, in the planning, you have to get the relevant parties to commit the human resources!
4. Installation of LoadRunner – This require administrative or power users privileges in order for installation to be successful.  That raise another set of questions: Will you be able to install LoadRunner in the premises?  Who can you look for to install the LoadRunner program?  Do you need clearance for installation?  Is the system being hardened to prevent installation?
5. Offshore Installation – Is offshore installation required for the load test setup?  Can you perform the installation via remote connection or do you require someone from the site to assist in the installation?
6. Running of JVM/.NET Probes for Diagnostics – This will require installation and instrumentation on the application server, meaning it will be intrusive to the system as a whole.  Do you require additional permissions for such installation?
7. Post-installation – Do remember to test if the installation is complete and the programs are working before moving on to the next phase.  Remember to do a connectivity check between the load generators to the controller to ensure they communicate prior the load test.
8. Working in different environments – Are you required to work in different stages of a load test project?  Example, you are required to run the test in (A) the  data center followed by (B) the local client segment and lastly (C) the remote client segment?  In this context, how do you ensure the scripts worked from A to C?  It will be easy if it is a change of hostnames and URL addresses that is being used in these environments as it can be achieved through parameterization.  But what if there are additional authentication mechanism introduced in environment B and C?  Authentication mechanisms such as additional cookie in the clients are added into the URL or 2-factor authentication can render the scripts developed in environment A useless!  How do you go about it?  Should you cater more time to re-script for the worst scenario or is it better to disable the authentication mechansim during the load test?

These are some basic considerations we usually asked our ourselves and clients.  Hope it will be useful in your planning.  What are other considerations make for a load test for you?

System\Context Switches/sec

This counter measures how frequently the processor has to switch from user-mode to kernel-mode to handle a request from a thread running in user mode. The heavier the workload running on your machine, the higher this counter will generally be, but over long term the value of this counter should remain fairly constant. If this counter suddenly starts increasing however, it may be an indicating of a malfunctioning device, especially if you are seeing a similar jump in the Processor(_Total)\Interrupts/sec counter on your machine.

You may also want to check Processor(_Total)\% Privileged Time counter and see if this counter shows a similar unexplained increase, as this may indicate problems with a device driver that is causing an additional hit on kernel mode processor utilization. Drill down using Process(instance)\% Processor Time counter for each process instances running on your machine. This won’t directly tell you which driver is utilizing processor time, but it may indicate which calling application is indirectly causing the problem and may help you troubleshoot the issue further.(Source: Mitch Tulloch, Windows Networking)

Processor(_Total)\Interrupts/sec

This counter measures the number of interrupts the processor have to respond over time. Interrupts are generated from hardware components like hard disk controller adapters and network interface cards. A sustained value over 1000 is usually an indication of a problem. Problems would include a poorly configured drivers, errors in drivers, excessive utilization of a device (like a NIC on an IIS server), or hardware failure. Compare this value with the System\Systems Calls/sec or System\Context Switches/sec. If the Interrupts/sec is much larger over a sustained period, you probably have a hardware issue. (Source: Microsoft TechNet)

So, what does System\Context Switches/sec represent?

A context switch occurs when the kernel switches the processor from one thread to another. A high rate of context switching means that the processor is being shared repeatedly between threads of the same priority (too many threads being generated from users or server that the processor spent time switching rather than performing useful work). (Source: Microsoft TechNet)

It’s a good idea to monitor System\Context Switches/sec over a period of time to establish a baseline for this counter. Why this is important, in the context of a load test, the System\Context Switches/sec will be collected as usual but you do not have a way of determining the acceptable threshold. A baseline of during its normal operation will greatly assist in analysing.