SNT Capacity Analysis
Capacity management is the process of apportioning limited resources among different workloads that are based on the time allotted to process each workload.
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In most systems, the instantaneous arrival rate of work exceeds the instantaneous processing capacity at certain times, thus some work must wait while other work is performed.
The longer the acceptable window of processing (response time, in communication terms) for each transaction relative to the actual time required to process, the fewer processing resources are required to support the workload. Conversely, the shorter the processing window, the greater the resource requirement. In other words, workloads with infinitely long processing times can be satisfied by systems with very small processing capabilities per unit time (on a mainframe these are background tasks). However, workloads with infinitely short processing times require an infinite amount of resources to satisfy (these are all the applications for which you are responsible).
In a network, available resources include:
- Processor power - both mainframe and communications control units
- Storage - both mainframe and CCU memory and mainframe peripheral storage (databases)
- Link bandwidth - most critical in the network backbone
It is the interrelationship of these resources that makes the projection of network capacity difficult. Some of these interrelations are the following:
- Insufficient processor power increases queuing, thus increasing the demand for storage and reducing the ability to utilize link bandwidth.
- Insufficient storage in one node increases its processor requirements and increases queuing in adjacent nodes, increasing their storage requirements. It also reduces the ability of all nodes to support increased link bandwidth.
- Insufficient link bandwidth increases storage requirements through increased queuing.
The network analyst must remember that a change to any node or link, either in capacity or workload, affects all adjacent nodes and the links attached to them.