Server Capacity Sizing

To successfully determine server sizes for an application:

- Define the load signature for each server.

- Determine throughput requirements using the formulas documented.

- Use the throughput requirements to estimate hardware requirements.

- Use the hardware requirements to construct sample applications configurations to test in isolated test conditions and later in the pilot project.

The load signature is determined by several factors, including:

- Number of optional applications features installed and in use on the server

- Location of middleware in the applications hierarchy (whether it communicates with legacy, COTS or web apps)

- Number of applications to be connected/installed

- Interface load

- Frequency of scheduled events

Data	Description
CPU Utilization	The percentage of CPU capacity used during a specific period of time.
Transaction throughout of the system	The average number of transactions completed during a specified period of time.
Average service time	The average time to complete a transaction.
Transaction capacity of the system	The number of transactions the server handles.
Average queue length	The average number of transactions in queue.
Average response time	The average time to respond to a transaction.

The table below lists the key system objects and counters to monitor. The values are recommended percentages.

Object	Counter	Instance	Comment
System	% Total Processor Time	Not applicable	Less than 80% means the level of processor performance is acceptable. Constant measurements above 95% mean there is cause for concern.
System	Processor Queue Length	Not applicable	Two or fewer means the level of processor performance is acceptable.
Thread	Context Switches/sec	_total	Lower is better. You measure the thread counter to enable the processor queue length counter.
Physical disk	% Disk Time	Each disk	Less than 80% means the level of physical disk performance is acceptable.
Physical disk	Current Disk Queue Length	Each disk	The count minus the number of spindles on the disks should average less than two. (A RAID device would have more than one spindle.)
Memory	Committed Bytes	Not applicable	If this value is smaller than the available amount of RAM, you have enough memory to support the running processes without excessive paging.
			If this value is consistently larger than available RAM, the computer is experiencing an unacceptable level of paging, and you must add more physical RAM
Memory	Page Reads/sec	Not applicable	Constant measurements greater than five indicate a requirement for more memory.
Database Server	Cache Hit Ratio	Not applicable	98% or greater is good because database queries are not delayed by paging off disk.
System	% Total Processor Time	Not applicable	Less than 80% means the level of processor performance is acceptable. Constant measurements above 95% mean there is cause for investigation.