Chapter 2. Resource Monitoring

19

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:

Page Ins/Page Outs

These statistics make it possible to gauge the flow of pages from system memory to attached

mass storage devices (usually disk drives). High rates for both of these statistics can mean that

the system is short of physical memory and is thrashing.

Active/Inactive Pages

These statistics show how heavily memory resident pages are used. A lack of inactive pages can

point toward a shortage of physical memory.

Free, Shared, Buffered, and Cached Pages

These statistics provide additional detail over the more simplistic active/inactive page statistics.

By using these statistics, it is possible to determine the overall mix of memory utilization.

Swap Ins/Swap Outs

These statistics show the system's overall swapping behavior. Excessive rates here can point to

physical memory shortages.

Successfully monitoring memory utilization requires a good understanding of how demand paged

virtual memory operating systems work. While such a subject alone could take up an entire book,

the basic concepts are discussed in Chapter 4 Physical and Virtual Memory. This chapter, along with

time spent monitoring a system, gives you the the necessary building blocks to learn more about this

subject.

2.4.4. Monitoring Storage

Monitoring storage normally takes place at two different levels:

Monitoring for sufficient disk space

Monitoring for storage related performance problems

The reason for this is that it is possible to have dire problems in one area, and no problems whatsoever

in the other. For example, it is possible to cause a disk drive to run out of disk space without once

causing any kind of performance related problems. Likewise, it is possible to have a disk drive that

has 99% free space, yet is being pushed past its limits in terms of performance.

However, it is more likely that the average system will experience varying degrees of resource short 

ages in both areas. Because of this, it is also likely that   to some extent   problems in one area will

impact the other. Most often this type of interaction takes the form of poorer and poorer I/O perfor 

mance as a disk drive nears 0% free space although, in cases of extreme I/O loads, it might be possible

to slow I/O throughput to such a level that applications will no longer run properly.

In any case, the following statistics are useful for monitoring storage:

Free Space

Free space is probably the one thing that all system administrators watch closely; it would be a

rare administrator that never checks on free space (or has some automated way of doing so).