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An iometer, or input/output (I/O) meter, is a tool that makes measurements on the performance of a computer’s I/O system, which includes the data buses, drives, and network interface. Via a graphical user interface, the iometer is also a troubleshooting tool that can help detect instances and possible causes of system I/O delays. Iometer benchmark information can help build better I/O drivers.
A computer’s I/O performance may be compared to athletic performance. In the iometer, a program that loads the I/O system is executed while making time and data volume measurements. In athletics, an obstacle course could be set up while a stopwatch is set to record the progress of the athlete at each stage. The iometer uses a client-server model for “loading” the I/O system to monitor and log performance metrics.
Data buses are used either exclusively by system devices or they may be shared. For instance, data bus latency, or the time it takes to reverse data direction, can be measured given various types of bus operations, including sharing data buses with other devices. An extended data and control bus that is typical of high-performance servers, for example, requires in-depth analysis to optimize bus data latency.
Hard drives are also used extensively by the central processing unit (CPU) and other system devices. Many factors affect the performance of hard drives as local drives or as network drives. For instance, when the contents of a drive are scattered in relatively far cylinders, the average access time increases noticeably.
Total I/O per second (TIOPS) suggests the capability of a computer system to respond to I/O requests. The iometer queues a benchmark I/O request rate, thus a computer system’s TIOPS is a basis for future I/O performance of the system. Total megabytes per second (TMBPS) is the number of bytes sent to or from the I/O per second, and a higher figure means the computer system has a faster overall response rate. A lower average I/O response time (AIORT) in milliseconds or thousandths of a second is ideal since less time is spent in waiting for the I/O system to respond.
Given a specific I/O loading condition, there will be a maximum I/O response time (MIORT) in milliseconds. This can indicate the major weakness in speed for the computer system. The MIORT usually occurs during shared I/O operations.
The percentage of CPU utilization (CPUUT) or the total CPUUT indicates how much of the computer capacity is being utilized. If the CPUUT is always 100% for easy I/O tasks, then a major change may be needed. This change may be in either the software or hardware configuration used in the computer system.
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