Testing UNIX system performance: Part 1
The iostat and sar utilities in UNIX analyze and report on I/O and CPU utilization and allocation, by providing a simultaneous interval by interval profile of disk and CPU usage. These utilities can provide indications of which system resource may be limiting overall system performance if used during heavy workloads or periods of inadequate system performance. When the system resource is identified, an administrator can then know what steps to take to improve system performance.
The following example is for the Solaris 2.X operating system. Since the presence and function of this utility varies slightly among different versions of UNIX, you should consult the UNIX System Administrator's manual for information about your specific system. The output from this utility can be redirected to a file for later analysis.
Iostat is the most useful utility for evaluating system performance while an RDBMS application is running. Properly configured, this utility will present disk I/O activity simultaneously with CPU loading.
The default mode for iostat displays only four drives. If the desired disks are known, the -D option (disk option) specifies these disks up to the default limit. If the desired disks are not known, -X option is used to display extended information on all disks.
When the utility has been run the resulting output will provide you with the following statistics:
rps = reads per second; wps = writes per second; util = percent utilization of your disk drives and ...
CPU utilization is given by:
us = cpu percentage running the user application
sy = cpu percentage used in system activities such as disk I/O or network management
wt = cpu percentage waiting for disk I/O to complete
id = cpu percentage not being used
Each line of the output will indicate the average number over the time interval. In most cases, five seconds should be the interval used when running iostat since the effect of averaging over longer intervals can mask critical information.
The sar utility will be discussed in a future tip.
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UNIX System Administration Handbook, 3/e
Author : Evi Nemeth, Garth Snyder and Trent R. Hein
Publisher : Prentice Hall
Published : Sep 2000
This major revision of the best-selling and single most comprehensive guide to UNIX system administration is ideal as both an introductory tutorial for those new to system administration and a day-to-day reference for "power administrators." Practical and hands-on in approach, it covers every aspect of system administration - from basic topics to UNIX esoterica - and provides explicit instructions for dealing with the six most popular versions of UNIX.