QUESTION:
1) I have issued a sar -q and I want to know: What signifies
a high (overloaded) run queue size?
.
2) I also issued a sar -r and I want to know what is a high/low
memory cycles?
.
3) The third question has to do with the iostat cmd.
What is balanced I/O and what is unbalanced I/O.
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A:
1. A very general value is an average at or near 10 for good
performance, however, this value really depends on the workload
(applications, processes, etc.). There is no reported or
documented value that can be used to indicate a high run queue size.
2. The value for the "cycle/s" statistic should average at or near
0 for good performance.
3. The "iostat" command is useful in determining whether a physical
volume has become a performance bottleneck and if there is potential
to improve the situation. The % utilization field for the physical
volumes ( tm_act) indicates how evenly the activity is spread
across the drives. If your workload's I/O is evenly distributed
around the system's disk drives then you have balanced I/O,
otherwise you have unbalanced I/O.
Utilization is the percentage of time a device is in use. General
queueing theory holds that devices with utilizations greater that
70% will see response time increases because incoming requests have
to wait for previous requests to complete.
Reference:
IBM Performance Monitoring and Tuning Guide (SC23-2365-01)
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This item was created from library item Q612881 BWPZT
Additional search words:
BWPZT IX JAN93 LPPS MEASURE OZNEW PERFORMANCE QUESTION RISCO
RISCSYSTEM SOFTWARE SUPT SYS SYSTEM TUNE
WWQA: ITEM: RTA000027786 ITEM: RTA000027786
Dated: 01/1995 Category: RISCO
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