36

Chapter 3. Bandwidth and Processing Power

3.3. Red Hat Linux Specific Information

Monitoring bandwidth and CPU utilization under Red Hat Linux entails using the tools discussed in

Chapter 2 Resource Monitoring; therefore, if you have not yet read that chapter, you should do so

before continuing.

3.3.1. Monitoring Bandwidth on Red Hat Linux

As stated in Section 2.4.2 Monitoring Bandwidth, it is difficult to directly monitor bandwidth utiliza 

tion. However, by looking at device level statistics, it is possible to roughly gauge whether insufficient

bandwidth is an issue on your system.

By using

vmstat

, it is possible to determine if overall device activity is excessive by viewing the

bi

and

bo

fields; in addition, taking note of the

si

and

so

fields give you a bit more insight into how

much disk activity is due to swap related I/O:

procs

memory

swap

io

system

cpu

r

b

w

swpd

free

buff

cache

si

so

bi

bo

in

cs

us

sy

id

1

0

0

0 248088 158636 480804

0

0

2

6

120

120

10

3

87

In this example, the

bi

field shows two blocks/second written to block devices (primarily disk drives),

while the

bo

field shows six blocks/second read from block devices. We can see that none of this

activity was due to swapping, as the

si

and

so

fields both show a swap related I/O rate of zero

kilobytes/second.

By using

iostat

, it is possible to gain a bit more insight into disk related activity:

Linux 2.4.18 18.8.0smp (raptor.example.com)

12/15/2002

avg cpu:

%user

%nice

%sys

%idle

5.34

4.60

2.83

87.24

Device:

tps

Blk_read/s

Blk_wrtn/s

Blk_read

Blk_wrtn

dev8 0

1.10

6.21

25.08

961342

3881610

dev8 1

0.00

0.00

0.00

16

0

This output shows us that the device with major number 8 (which is

/dev/sda

, the first SCSI disk)

averaged slightly more than one I/O operation per second (the

tsp

field). Most of the I/O activity for

this device were writes (the

Blk_wrtn

field), with slightly more than 25 blocks written each second

(the

Blk_wrtn/s

field).

If more detail is required, use

iostat

's

 x

option:

Linux 2.4.18 18.8.0smp (raptor.example.com)

12/15/2002

avg cpu:

%user

%nice

%sys

%idle

5.37

4.54

2.81

87.27

Device:

rrqm/s wrqm/s

r/s

w/s

rsec/s

wsec/s

rkB/s

wkB/s avgrq sz

/dev/sda

13.57

2.86

0.36

0.77

32.20

29.05

16.10

14.53

54.52

/dev/sda1

0.17

0.00

0.00

0.00

0.34

0.00

0.17

0.00

133.40

/dev/sda2

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

11.56

/dev/sda3

0.31

2.11

0.29

0.62

4.74

21.80

2.37

10.90

29.42

/dev/sda4

0.09

0.75

0.04

0.15

1.06

7.24

0.53

3.62

43.01

Over and above the longer lines containing more fields, the first thing to keep in mind is that

iostat

is now displaying statistics on a per partition level. By using

df

to associate mount points with device