Lowe D. Networking For Dummies

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Book III

Chapter 7

Solving Network

Problems

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Documenting Your Trials and Tribulations

to see whether the problem generated a noteworthy event. In many cases,

the event logs contain an entry that pinpoints the exact cause of the prob-

lem and suggests a solution.

To display the event logs in a Windows server, use Event Viewer, which is

available from the Administrative Tools menu. For example, Figure 7-5 shows

an Event Viewer from a Windows Server 2008 system. The tree listing on

the left side of Event Viewer lists five categories of events that are tracked:

Application, Security, System, Directory Service, and File Replication Service.

Select one of these options to see the log that you want to view. For details

about a particular event, double-click the event to display a dialog box with

detailed information about the event.

Figure 7-5:

Event

Viewer.

Documenting Your Trials and Tribulations

For a large network, you probably want to invest in problem-management

software that tracks each problem through the entire process of trouble-

shooting, from initial report to final resolution. For small- and medium-sized

networks, it’s probably sufficient to put together a three-ring binder with

pre-printed forms. Or record your log in a Word document or an Excel

spreadsheet.

Regardless of how you track your network problems, the tracking log should

include the following information:

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Documenting Your Trials and Tribulations

✦ The real name and the network username of the person reporting the

problem

✦ The date the problem was first reported

✦ An indication of the severity of the problem

Is it merely an inconvenience, or is a user unable to complete his or her

work because of the problem? Does a workaround exist?

✦ The name of the person assigned to resolve the problem

✦ A description of the problem

✦ A list of the software involved, including versions

✦ A description of the steps taken to solve the problem

✦ A description of any intermediate steps that were taken to try to solve

the problem, along with an indication of whether those steps were

“undone” when they didn’t help solve the problem

✦ The date the problem was finally resolved

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Chapter 8: Network Performance

Anxiety

In This Chapter

✓ Understanding performance problems

✓ Looking at bottlenecks

✓ Developing a procedure for solving performance problems

✓ Monitoring performance

✓ Implementing other tips for speeding up your network

he term network performance refers to how efficiently the network

responds to users’ needs. It goes without saying that any access to

resources that involves a network will be slower than similar access that

doesn’t involve a network. For example, it takes longer to open a Word

document that resides on a network file server than it takes to open a simi-

lar document that resides on a user’s local hard drive. However, it shouldn’t

take much longer. If it does, you have a network performance problem.

This chapter is a general introduction to the practice of tuning your network

so that it performs as well as possible. Keep in mind that many specific bits

of network tuning advice are scattered throughout this book. In this chap-

ter, you can find some specific techniques for analyzing your network’s per-

formance, taking corrective action when a performance problem develops,

and charting your progress.

Why Administrators Hate Performance Problems

Network performance problems are among the most difficult network prob-

lems to track down and solve. If a user simply can’t access the network, it

usually doesn’t take long to figure out why: A cable is broken, a network

card or hub is malfunctioning, a user doesn’t have permission to access the

resource, and so on. After a little investigation, the problem usually reveals

itself. You fix it and move on to the next problem.

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What Exactly Is a Bottleneck?

Unfortunately, performance problems are messier. Here are just a few of the

reasons that network administrators hate performance problems:

✦ Performance problems are difficult to quantify. Exactly how much

slower is the network now than it was a week ago, a month ago, or even

a year ago? Sometimes the network just feels slow, but you can’t quite

define exactly how slow it really is.

✦ Performance problems usually develop gradually. Sometimes, a net-

work slows down suddenly and drastically. More often, though, the net-

work gradually gets slower, a little bit at a time, until one day when the

users notice that the network is slooow.

✦ Performance problems often go unreported. Users gripe about the

problem to each other around the water cooler, but they don’t for-

mally contact you to let you know that their network seems 10 percent

slower than usual. As long as they can still access the network, they just

assume that the problem is temporary or just in their imaginations.

✦ Many performance problems are intermittent. Sometimes, a user

calls you and complains that a certain network operation has become

slower than molasses — and by the time you get to the user’s desk,

the operation performs like a snap. Sometimes, you can find a pattern

to the intermittent behavior, such as it’s slower in the morning than in

the afternoon, or it’s only slow while backups are running or while the

printer is working. Other times, you can’t find a pattern. Sometimes the

operation is slow; sometimes it isn’t.

✦ Performance tuning is not an exact science. Improving performance

sometimes involves educated guesswork. Will upgrading all the users

from 100 Mbps to gigabit Ethernet improve performance? Probably.

Will segmenting the network improve performance? Maybe. Will adding

another 4GB of RAM to the server improve performance? Hopefully.

✦ The solution to performance problems is sometimes a hard sell. If a

user can’t access the network because of a malfunctioning component,

there’s usually not much question that the purchase of a replacement is

justified. However, if the network is slow and you think you can fix it by

upgrading the entire network to gigabit Ethernet, you may have trouble

selling management on the upgrade.

What Exactly Is a Bottleneck?

The term bottleneck does not in any way refer to the physique of your typi-

cal computer geek. (Well, I guess it could, in some cases.) Rather, computer

geeks coined the phrase when they discovered that the tapered shape of a

bottle of Jolt Cola limited the rate at which they could consume the beverage.

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Performance

Anxiety

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What Exactly Is a Bottleneck?

“Hey,” a computer geek said one day, “the gently tapered narrowness of this

bottle’s neck imposes a distinct limiting effect upon the rate at which I can

consume the tasty caffeine-laden beverage contained within. This draws to

mind a hitherto undiscovered yet obvious analogy to the limiting effect that a

single slow component of a computer system can have upon the performance

of the system as a whole.”

“Fascinating,” replied all the other computer geeks, who were fortunate

enough to be present at that historic moment.

The term stuck and is used to this day to draw attention to the simple fact

that a computer system is only as fast as its slowest component. It’s the

computer equivalent of the old truism that a chain is only as strong as its

weakest link.

For a simple demonstration of this concept, consider what happens when

you print a word processing document on a slow printer. Your word pro-

cessing program reads the data from disk and sends it to the printer. Then

you sit and wait while the printer prints the document.

Would buying a faster CPU or adding more memory make the document

print faster? No. The CPU is already much faster than the printer, and your

computer already has more than enough memory to print the document.

The printer itself is the bottleneck, so the only way to print the document

faster is to replace the slow printer with a faster one.

Here are some other random thoughts about bottlenecks:

✦ A computer system always has a bottleneck. For example, suppose that

you decided that the bottleneck on your file server is a slow IDE hard

drive, so you replace it with the fastest SCSI drive money can buy. Now,

the hard drive is no longer the bottleneck: The drive can process infor-

mation faster than the controller card to which the disk is connected.

You haven’t really eliminated the bottleneck: You just moved it from the

hard drive to the disk controller. No matter what you do, the computer

will always have some component that limits the overall performance of

the system.

✦ One way to limit the effect of a bottleneck is to avoid waiting for the

bottleneck. For example, print spooling lets you avoid waiting for a slow

printer. Spooling doesn’t speed up the printer, but it does free you to do

other work while the printer chugs along. Similarly, disk caching lets you

avoid waiting for a slow hard drive.

✦ One of the reasons computer geeks are switching from Jolt Cola to

Snapple is that Snapple bottles have wider necks.

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The Five Most Common Network Bottlenecks

Direct from the home office in sunny Fresno, California, here are the ten —

oops, five — most common network bottlenecks, in no particular order.

The hardware inside your servers

Your servers should be powerful computers capable of handling all the work

your network will throw at them. Don’t cut corners by using a bottom-of-the-

line computer that you bought at a discount computer store.

The following are the four most important components of your server

hardware:

✦ Processor: Your server should have a powerful processor. As a general

rule, any processor that’s available in a $500 computer from a store

that sells TVs and washing machines as well as computers is not a

processor that you want to see in your file server. In other words,

avoid processors that are designed for consumer-grade home comput-

ers. For optimum performance, your servers should use server-class

Itanium or Xeon processors.

✦ Memory: You can’t have too much memory. Memory is cheap, so don’t

skimp. Don’t even think about running a server with less than 8GB of RAM.

✦ Disk: Don’t mess around with inexpensive SATA hard drives. To be

respectable, you should have nothing but SCSI drives.

✦ Network interface: A $9.95 network card might be fine for your home

network, but don’t use one in a file server that supports 50 users and

then expect to be happy with the server’s performance. Remember that

the server computer uses the network a lot more than any of the clients,

so equip your servers with good network cards.

The server’s configuration options

All network operating systems have options that you can configure. Some

of these options can make the difference between a pokey network and a

zippy network. Unfortunately, no hard-and-fast rules exist for setting these

options. Otherwise, you wouldn’t have options.

The following are some of the more important tuning options available for

most servers:

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The Five Most Common Network Bottlenecks

✦ Virtual memory options: Virtual memory refers to disk paging files that

the server uses when it doesn’t have enough real memory to do its work.

Few servers ever have enough real memory, so virtual memory is always

an important server feature. You can specify the size and location of the

virtual memory paging files. For best performance, you should provide

at least 1.5 times the amount of real memory. For example, if you have

16GB of real memory, allocate at least 24GB of virtual memory. If neces-

sary, you can increase this size later.

✦ Disk striping: Use Disk Defragmenter to optimize the data storage on

your server’s disks. If the server has more than one hard drive, you

can increase performance by creating striped volumes, which allow

disk I/O operations to run concurrently on each of the drives in the

stripe set.

✦ Network protocols: Make sure that your network protocols are config-

ured correctly; remove any protocols that aren’t necessary.

✦ Free disk space on the server: Servers like to have plenty of breath-

ing room on their disks. If the amount of free disk space on your server

drops precipitously low, the server chokes up and slows to a crawl.

Make sure that your server has plenty of space: A few dozen GBs of

unused disk space provide a healthy buffer.

Servers that do too much

One common source of network performance problems is servers that are

overloaded with too many duties. Just because modern network operating

systems come equipped with dozens of different types of services doesn’t

mean that you should enable and use them all on a single server. If a single

server is bogged down because of too much work, add a second server

to relieve the first server of some of its chores. Remember the old saying:

“Many hands make light work.”

For example, if your network needs more disk space, consider adding

a second file server rather than adding another drive to the server that

already has four drives that are nearly full. Or better yet, purchase a file

server appliance that is dedicated just to the task of serving files.

As a side benefit, your network will be easier to administer and more reliable

if you place separate functions on separate servers. For example, if you have

a single server that doubles as a file server and a mail server, you’ll lose

both services if you have to take down the server to perform an upgrade or

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The Five Most Common Network Bottlenecks

repair a failed component. However, if you have separate file and mail server

computers, only one of the services will be interrupted if you have to take

down one of the servers.

The network infrastructure

A network infrastructure comprises the cables and any switches, hubs, rout-

ers, and other components that sit between your clients and your servers.

The following network infrastructure items can slow down your network:

✦ Switches: Because switches are so inexpensive now, you can afford-

ably solve a lot of performance problems by replacing outdated hubs

with switches. Using switches instead of hubs reduces the overall load

on your network. Also, make sure that your switches can handle the

performance requirements of your network. For best performance, the

switches should have gigabit ports.

✦ Segment sizes: Keep the number of computers and other devices on

each network segment to a reasonable number. About 20 devices is

usually the right number. (Note that if you replace your old hubs with

switches, you instantly cut the size of each segment because each port

on a switch constitutes a separate segment.)

✦ The network’s speed: If you have an older network, you’ll probably dis-

cover that many — if not all — of your users are still working at 100 Mbps.

Upgrading to gigabit speed will speed up the network dramatically.

✦ The backbone speed: If your network uses a backbone to connect seg-

ments, consider upgrading the backbone to 1 Gbps.

The hardest part about improving the performance of a network is determin-

ing what the bottlenecks are. With sophisticated test equipment and years of

experience, network gurus can make pretty good educated guesses. Without

the equipment and experience, you can still make pretty good uneducated

guesses.

Malfunctioning components

Sometimes a malfunctioning network card or other component slows down

the network. For example, a switch may malfunction intermittently, occa-

sionally letting packets through but dropping enough of them to slow down

the network. After you identify the faulty component, replacing it will restore

the network to its original speed.

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Network

Performance

Anxiety

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Tuning Your Network the Compulsive Way

You have two ways to tune your network. The first is to think about it a bit,

take a guess at what may improve performance, try it, and see whether the

network seems to run faster. This approach is how most people go about

tuning the network.

Then you have the compulsive way, which is suitable for people who orga-

nize their sock drawers by color and their food cupboards alphabetically by

food groups. The compulsive approach to tuning a network goes something

like this:

1. Establish a method for objectively testing the performance of some

aspect of the network.

This method is benchmarking, and the result of your benchmark is a

baseline.

2. Change one variable of your network configuration and rerun the test.

For example, suppose you think that increasing the size of the disk

cache can improve performance. Change the cache size, restart the

server, and run the benchmark test. Note whether the performance

improves, stays the same, or becomes worse.

3. Repeat Step 2 for each variable that you want to test.

Here are some salient points to keep in mind if you decide to tune your net-

work the compulsive way:

✦ If possible, test each variable separately. In other words, reverse the

changes you made to other network variables before proceeding.

✦ Write down the results of each test. That way, you have an accurate

record of the impact that each change made on your network’s

performance.

✦ Be sure to change only one aspect of the network each time you run

the benchmark. If you make several changes, you won’t know which one

caused the change. One change may improve performance, but the other

change may worsen performance so that the changes cancel each other

out — kind of like offsetting penalties in a football game.

✦ If possible, conduct the baseline test during normal working hours.

That way, the network is undergoing its normal workload.

✦ To establish your baseline performance, run your benchmark test two

or three times to make sure that the results are repeatable.

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Monitoring Network Performance

One way to monitor network performance is to use a stopwatch to see how

long it actually takes to complete common network tasks, such as opening

documents or printing reports. If you choose to monitor your network by

using the stopwatch technique, you’ll want to get a clipboard, baseball cap,

and gray sweat suit to complete the ensemble.

A more high-tech approach to monitoring network performance is to use a

monitor program that automatically gathers network statistics for you. After

you set up the monitor, it plugs away, silently spying on your network and

recording what it sees in performance logs. You can then review the perfor-

mance logs to see how your network is doing.

For large networks, you can purchase sophisticated monitoring programs

that run on their own dedicated servers. For small- and medium-sized net-

works, you can probably get by with the built-in monitoring facilities that

come with the network operating system. For example, Figure 8-1 shows

the Performance Monitor tool that comes with Windows Server 2003. Other

operating systems come with similar tools.

Figure 8-1:

Monitoring

performance.

Windows Performance Monitor lets you keep track of several different

aspects of system performance at once. You track each performance aspect

by setting up a counter. You can choose from dozens of different counters.

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