What is a Backup

8/6/2019 What is a Backup

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Chapter Overview

Backups

Antivirus Policies

Patches and Updates


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What Is a Backup? Backups are copies of data that you make on a regular basis,

allowing you to restore lost data in a timely manner.

Even if you have other storage technologies in place that

provide fault tolerance, you still need a backup solution. Networks both complicate and simplify the process of making

regular backups. More complicated because you have data stored on multiple

devices that must be protected

Simpler because you can use the network to access those devices

A network backup strategy specifies what data you back up,how often you back it up, and what medium you use to storethe backups.

The backup hardware, software, and administrative policies youwill use depend on how much data you have to back up, howmuch time you have to back it up, and how much protectionyou want to provide.


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Selecting a Backup Drive

Try to automate as much of the backup process aspossible.

Select a device that can store all of your data withoutfrequent media changes.

Consider the speed at which the drive writes data tothe medium.

The amount of time that you have to perform your

backups is sometimes called the backup window. The backup device that you choose should depend in

part on The amount of data you have to protect

The amount of time that you have to back it up


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Determining Backup Costs Cost is always a factor in selecting a hardware product.

Faster drives are generally more expensive.

A low-end backup drive can cost $100 to $200, which is suitable for

backing up a home computer where speed is not a major factor. High-end backup drives can have prices that run into five figures.

When you evaluate backup devices, be aware of the productsmedia costs as well.

Some products might seem economical because the drive isinexpensive, but in the long run they might not be, because themedia are so expensive.

Determine the cost per megabyte of the storage a driveprovides. Divide the price of the medium by the number of megabytes it can

store, and use this figure to compare the relative cost of variousdevices.


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Selecting a Drive Interface Backup devices can use any of the standard computer

interfaces: Integrated Drive Electronics (IDE), universalserial bus (USB), or Small Computer System Interface

(SCSI). The most common interface used in high-end network

backup solutions is SCSI. SCSI devices operate more independently than IDE devices, which

means that the backup process is more efficient.

SCSI devices can maintain a queue of commands that they havereceived from the host adapter and can execute them sequentially

and independently.

When multiple IDE devices share a channel, only oneoperates at a time.

Magnetic tape drives require a consistent stream of data

to write to the tape with maximum effectiveness.


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A Typical Magnetic Tape Drive


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Magnetic Tape Drives Magnetic tape drives are the most common hardware

devices used to back up data.

Tape drives are not random access devices. You cannot mount a tape drive in a computers file system, assign

it a drive letter, and copy files to it, as you can with a hard diskdrive.

A special software program is required to address thedrive and send the data you select to it for storage.

Magnetic tape drives are well suited for backups, and theyoffer several advantages: Fast

Hold a lot of data

Low media cost, often less than one-half cent per megabyte

Tape drives are useless for anything other than backups.


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Magnetic Tape Technologies

Type TapeWidth

Cartridge Size Capacity(Uncompressed)

Speed

Quarter-inchcartridge (QIC)

0.25 in. 4 6 0.625 in. (datacartridge); 3.25 2.5 0.6 in.(minicartridge)

Up to 20 GB 2 to 120MB/min.

Digital audiotape (DAT)

4 mm 2.875 2.0625 0.375 in. Up to 20 GB 3 to 144MB/min.

8 mm 8 mm 3.7 2.44 0.59 in. Up to 60 GB Up to 180MB/min.

Digital lineartape (DLT)

0.50 in. 4.16 4.15 1 in. Up to 40 GB Up to 360MB/min.

Linear tape-open (LTO),Ultrium media

0.50 in. 4.0 4.16 0.87 in. Up to 100 GB Up to 1920MB/min.


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CD-ROM Drives Writable CD-ROM drives, such as compact disc-

recordables (CD-Rs) and compact disc rewritables(CD-RWs), can be used as backup devices.

Advantages The low cost of the media makes CDs an economical

solution.

Many computers already have CD-ROM drives, whicheliminates the need to buy a dedicated backup drive.

Disadvantages By backup device standards, the capacity of a CD is low,

about650 MB.

For network backups, CD-ROMs are usually inadequate.

Network backup software products usually do not recognize

CD-R and CD-RW drives.


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Cartridge Drives Removable cartridge drives, such as Iomegas Zip

and Jaz drives, can be used for backups. Zip cartridges hold only 100 MB or 250 MB, which makes

them less practical than CDs for backups. Jaz drives are available in 1-GB and 2-GB versions, which is

sufficient for a backup device.

Cartridge drives mount into a computers file system. You can assign a drive letter to a cartridge drive and copy

files to it just as you can assign a drive letter and copy filesto a hard drive.

Disadvantage: the cost of the media is extremelyhigh, making cartridge drives impractical for networkbackups.


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A Typical Autochanger


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Autochangers An autochanger is a unit that contains one or more drives

and a robotic mechanism that swaps the media in and outof the drives. Some autochangers are small devices with a single drive and an

array that holds four or five tapes.

Others are enormous devices with as many as four drives and anarray of 100 tapes or more.

When a backup job fills one tape (or other storagemedium), the mechanism extracts it from the drive andinserts another, and the job continues.

If you buy a large enough autochanger, you can create along-term backup strategy that allows backups to runcompletely unattended for weeks at a time.

Autochanger prices can be astonishingly high, reaching asmuch as six figures in some cases.


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Target Selection

The most basic function of a backup softwareprogram is to let you select what you want to

back up, sometimes called the target. A good backup program enables you to select

targets by selecting

Entire computers

Specific drives on those computers

Specific directories on the drives

Specific files in specific directories


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The Backup Dialog Box in the

Windows 2000 Backup Program


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Full, Incremental, and Differential

Backups A full backup copies the entire contents of a computers

drives to tape or another medium.

When you perform a full backup every day, most of the

files you are writing to the tape are exactly the same asthey were the previous day.

Between full backups, administrators perform specialtypes of filtered jobs that back up only the recentlymodified files. An incremental job backs up only the files changed since the last

backup job of any kind.

A differential job backs up only the files that have changed sincethe last full backup.

The backup software filters the files for backup jobs byusing a special file attribute called the archive bit, which is

on every file on the computer.


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Archive Bits The archive bit for a file is activated by any application that

modifies that file.

When the backup program scans the target drive during anincremental or differential job, it selects for backup only the fileswith active archive bits.

During a full backup, the software backs up the entire contentsof a computers drives, and also resets the archive bit on all ofthe files.

As work on the computer proceeds after the backup job is

completed, files are modified, and the archive bits for themodified files are activated.

The next day, you can run an incremental or differential backupjob, which filters out all files that do not have an active archive

bit.

Compared to a full backup, an incremental or differential backup

job is usually much smaller, so it takes less time and less tape.


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Incremental Jobs Incremental jobs reset the archive bits on the files

they back up.

When you run an incremental job, you back up only

the files that have changed since the last backup,whether it was a full backup or an incrementalbackup.

If you restore an entire computer, you must firstperform a restore from the last full backup tape, and

then restore each incremental job performed sincethe last full backup.

The order of the restore jobs is essential if you wantthe computer to have the latest version of every file. Advantage: uses the least amount of tape

Disadvantage: lengthens the restore process


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Differential Jobs

Differential jobs do not reset the archive biton the files they back up.

Every differential job backs up all of the filesthat have changed since the last full backup.

Advantage: differential backups simplify therestore process.

Disadvantage: differential backups use more tape,because some of the same files are backed upeach day.


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Scheduling All backup products let you create a backup job and execute it

immediately.

The key to automating a backup routine is being able toschedule jobs to execute unattended.

Scheduled jobs can run when the office is closed and thenetwork is idle.

Not all of the backup programs supplied with operating systemsor designed for stand-alone computers will support scheduling,but all network backup software products do.

Backup programs use various methods to automatically executebackup jobs.

You specify whether you want to execute the job once orrepeatedly at a specified time each day, week, or month.

After creating a logical sequence of backup jobs that execute bythemselves at regular intervals, you only need to change thetape in the drive each day.


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The Schedule Job Dialog Box in the



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Logging and Cataloging Most backup software products can maintain a log of

the backup process as it occurs. You can often specify a level of detail for the log.

You should periodically check the log, which tells you When selected files are skipped for any reason

When errors occur on either the backup drive or one of thecomputers involved in the backup process

Backup software programs also catalog the files they

back up, which facilitates the process of restoringfiles later. The catalog is a list of every file that the software has

backed up during each job.

To restore files from the backup medium, you browsethrough the catalog and select the files, directories, or drivesthat you want to restore.


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Media Rotation Using new tapes for every backup job and storing them all

permanently can become extremely expensive. It is more common to reuse backup tapes.

To reuse tapes properly, you must carefully plan your mediarotation scheme.

The Grandfather-Father-Son media rotation scheme refers tobackup jobs that run monthly, weekly, and daily, and it requiresyou to maintain A set of tapes for daily jobs, which you reuse every week

A set of weekly tapes, which you reuse every month A set of monthly tapes, which you reuse every year

When the software program implements the rotation scheme, it Provides a basic schedule for the jobs

Tells you what name to write on each tape as you use it

Tells you which tape to put in the drive for each job


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Restoring You must perform periodic test restores from

your backup tapes or other media to ensure that

you can recover any lost data. Even if all your jobs are completed successfully and

your log files show that all of your data has beenbacked up, there is no better test of a backup systemthan an actual restore.

Most of the restore jobs you will perform will berestoring only one or a few files that a user hasdeleted. A backup program with a database that lets you search

for a specific file makes your job much easier and

enables you to restore any file in minutes.


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The Restore Dialog Box in the



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Network Backup Functions Choose a backup software product that is designed for

network use.

A network backup software product differs from an

application designed for stand-alone systems in that thenetwork product can back up other computers on thenetwork.

A fully functional network backup product can back updrives anywhere on the network, plus important operating

system features on other computers, such as the WindowsRegistry and directory service databases.

Network backup products often have optional add-oncomponents that let you perform specialized backup tasks,such as backing up live databases or computers runningother operating systems.


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What Is a Virus? A virus is a software routine that is deliberately designed

to attach itself to another piece of software on acomputer, perform some preprogrammed activity, and

spread to other computers on the network. The worst types of viruses are engineered to irretrievably destroy

all or part of the data stored on the computer by wiping out harddrives.

Potentially damaging programs such as viruses, Trojan horses, andworms can find their way onto a network through file downloads,

e-mails, or even removable disks. Like biological viruses, computer viruses are designed to

replicate themselves by infecting other pieces of software.

A virus on an infected removable disk can migrate to thecomputers hard drive and infect the code on the hard

drive.


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How Viruses Can Spread Throughout

a Network


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Virus Types

Boot sector viruses

Executable file viruses

Polymorphic viruses

Stealth viruses

Macro viruses

Worms Trojan horses


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Preventing Virus Infections All users should be wary of removable disks from outside

sources and particularly of files attached to e-mailmessages.

You should use antivirus software products to protectindividual computers.

A virus scanner works by examining files and searching forspecific code signatures that are peculiar to certainviruses.

The scanner has a library of virus definitions that it uses to identifyviruses.

To keep your computers fully protected, you must update the virussignatures for your program on a regular basis.

Antivirus programs designed for use on networks do notprovide greater protection against viruses, but they

simplify the process of implementing the protection.


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Major Updates Even a computer with a relatively simple

configuration can have many different softwarecomponents that are regularly updated.

Years ago, operating systems manufacturers wouldrelease many different software patches, eachaddressing a specific issue.

Now manufacturers release groups of updates in asingle package. This practice was pioneered by Microsoft with its Service

Pack releases for MicrosoftWindows NT.

Each Service Pack release for a product contains a collectionof patches and updates, all of which are applied by oneinstallation program.

Because the various patches have all been tested together,the operating system environment is consistent.


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Patches Between the releases of Service Packs or other major

software updates, manufacturers may also makeindividual patches available.

A patch is usually a small fix that is designed to address ahighly specific problem.

In some cases, manufacturers recommend that you installa patch only under certain conditions, such as when youare using a particular combination of components or when

you are experiencing a specific error. If your environment does not qualify, do not assume that you

should install the patch anyway, just to keep your software current.

Read all of the release documentation and carefully followthe manufacturers instructions.


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Software Upgrades and Updates Software manufacturers typically release periodic

upgrades.

An update is usually a relatively minor release thataddresses specific issues or provides modestenhancements.

An upgrade is a major release that provides newfeatures and capabilities.

In most cases, patches and updates are free, but youmust buy an upgrade.

The cumulative cost of the upgrade process can beenormous.

If you do not need new features, it might not be

worth upgrading.


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Chapter Summary

Backups Magnetic tape is the most popular storage medium for

backups.

Backup software enables you to select the data youwant to back up and sends it to the device you use forbackups.

Daily backup jobs can be full backups, incrementalbackups, or differential backups.

A good backup software program allows you toschedule jobs to execute at any time.

Network backup software enables you to back up datafrom computers anywhere on the network, and mightalso provide optional features such as live database

backups.


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Chapter Summary (Cont.) Antivirus policies

Viruses are dangerous programs that can damage

the data on a computer and spread to the othercomputers on a network.

To protect your network against viruses, you mustrun antivirus software on every computer.

Patches and updates Obtaining, evaluating, and deploying software

patches and updates is an important part of thenetwork administrators job.

Software upgrades are major undertakings thatcan be extremely expensive and time-consuming.

What is a Backup

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