Monitoring Bandwidth; Monitoring Memory - Red Hat ENTERPRISE LINUX 3 - INTRODUCTION TO SYSTEM ADMINISTRATION Administration Manual

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I/O processing, and so on. These statistics also reveal that, when system performance is monitored,
there are no boundaries between the different statistics. In other words, CPU utilization statistics may
end up pointing to a problem in the I/O subsystem, or memory utilization statistics may reveal an
application design flaw.
Therefore, when monitoring system performance, it is not possible to examine any one statistic in
complete isolation; only by examining the overall picture it it possible to extract meaningful informa-
tion from any performance statistics you gather.

2.4.2. Monitoring Bandwidth

Monitoring bandwidth is more difficult than the other resources described here. The reason for this
is due to the fact that performance statistics tend to be device-based, while most of the places where
bandwidth is important tend to be the buses that connect devices. In those instances where more than
one device shares a common bus, you might see reasonable statistics for each device, but the aggregate
load those devices place on the bus would be much greater.
Another challenge to monitoring bandwidth is that there can be circumstances where statistics for
the devices themselves may not be available. This is particularly true for system expansion buses
2
and datapaths . However, even though 100% accurate bandwidth-related statistics may not always be
available, there is often enough information to make some level of analysis possible, particularly when
related statistics are taken into account.
Some of the more common bandwidth-related statistics are:
Bytes received/sent
Network interface statistics provide an indication of the bandwidth utilization of one of the more
visible buses — the network.
Interface counts and rates
These network-related statistics can give indications of excessive collisions, transmit and receive
errors, and more. Through the use of these statistics (particularly if the statistics are available
for more than one system on your network), it is possible to perform a modicum of network
troubleshooting even before the more common network diagnostic tools are used.
Transfers per Second
Normally collected for block I/O devices, such as disk and high-performance tape drives, this
statistic is a good way of determining whether a particular device's bandwidth limit is being
reached. Due to their electromechanical nature, disk and tape drives can only perform so many
I/O operations every second; their performance degrades rapidly as this limit is reached.

2.4.3. Monitoring Memory

If there is one area where a wealth of performance statistics can be found, it is in the area of moni-
toring memory utilization. Due to the inherent complexity of today's demand-paged virtual memory
operating systems, memory utilization statistics are many and varied. It is here that the majority of a
system administrator's work with resource management takes place.
The following statistics represent a cursory overview of commonly-found memory management statis-
tics:
2. More information on buses, datapaths, and bandwidth is available in Chapter 3 Bandwidth and Processing
Power.
Chapter 2. Resource Monitoring