Installation Techniques

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INFORMATION SHEET 1.3Structure of operating systems

Operating – System Structures

An operating system provides the environment within which programs are executed.

Internally, operating systems vary greatly in their makeup, since they are organized along manydifferent lines. The design of a new operating system is a major task. It is important that thegoals of the system e well defined efore the design egins. These goals form the asis for choices among various algorithms and strategies.

!e can view an operating system from several vantage points. "ne view focuses on theservices that the system provides# another, on the interface that it makes availale to users andprogrammers# a third, on its components and their interconnections. In this section we exploreall three aspects of operating systems, showing the viewpoints of users, programmers, andoperating$system designers. !e consider what services an operating system provides, howthey are provided, and what the various methodologies are for designing such systems. %inally,we descrie how operating systems are created and how a computer starts its operatingsystem.

1.3.1 Operating-System Services

An operating system provides an environment for the execution of programs. It providescertain services to programs and to the users of those programs. The specific servicesprovided, of course, differ from one operating system to another, ut we can identify commonclasses. These operating$system services are provided for the convenience of the programmer,to make the programming task easier.

"ne set of operating$system services provides functions that are helpful to the user.& ser inter!ace. Almost all operating systems have a user inter!ace "I#. This interface

can take several forms. "ne is a c$mman%-&ine inter!ace "'(I#, which uses text

commands and a method for entering them 'say, a program to allow entering and editingof commands(. Another is a )atc* inter!ace, in which commands and directives tocontrol those commands are entered into files, and those files are executed. )ostcommonly, a grap*ica& user inter!ace "+I# is used. *ere, the interface is a windowsystem with a pointing device to direct I+", choose from menus, and make selectionsand a keyoard to enter text.

& ,r$gram eecuti$n. The system must e ale to load a program into memory and torun that program. The program must e ale to end its execution, either normally or anormally 'indicating error(.

& IO $perati$ns. A running program may reuire I+", which may involve a file or an I+"device. %or specific devices, special functions may e desired 'such as recording to a- or / drive or lanking a -0T screen(. %or efficiency and protection, users usually

cannot control I+" devices directly. Therefore, the operating system must provide ameans to do I+".& Fi&e-system manipu&ati$n. The file system is of particular interest. "viously, programs

need to read and write files and directories. They also need to create and delete them yname, search for a given file, and list file information. %inally, some programs includepermissions management to allow or deny access to files or directories ased on fileownership.

& '$mmunicati$ns. There are many circumstances in which one process needs toexchange information with another process. Such communication may occur etween


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processes that are executing on the same computer or etween processes that areexecuting on different computer systems tied together y a computer network.-ommunications may e implemented via shared memory or through message passing,in which packets of information are moved etween processes y the operating system.

/ Err$r %etecti$n. The operating system needs to e constantly aware of possile errors.1rrors may occur in the -23 and memory hardware 'such as a memory error or a power

failure(, in I+" devices 'such as a parity error on tape, a connection failure on a network,or lack of paper in the printer(, and in the user program 'such as an arithmetic overflow,an attempt to access an illegal memory location, or a too$great use of -23 time(. %or each type of error, the operating system should take the appropriate action to ensurecorrect and consistent computing. eugging facilities can greatly enhance the user4sand programmer4s ailities to use the system efficiently.

Another set of operating$system functions exists not for helping the user ut rather for ensuring the efficient operation of the system itself. Systems with multiple users can gainefficiency y sharing the computer resources among the users.

& Res$urce a&&$cati$n. !hen there are multiple users or multiple jos running at thesame time, resources must e allocated to each of them. )any different types of resources are managed y the operating system. Some 'such as -23 cycles, mainmemory, and file storage( may have special allocation code, whereas others 'such asI+" devices( may have much more general reuest and release code. %or instance, indetermining how est to use the -23, operating systems have -23$scheduling routinesthat take into account the speed of the -23, the jos that must e executed, the numer of registers availale, and other factors. There may also e routines to allocate printers,modems, 3S5 storage drives, and other peripheral devices.

& Acc$unting. !e want to keep track of which users use how much and what kinds of computer resources. This record keeping may e used for accounting 'so that users cane illed( or simply for accumulating usage statistics. 3sage statistics may e a valualetool for researchers who wish to reconfigure the system to improve computing services.

/ ,r$tecti$n an% security. The owners of information stored in a multiuser or networkedcomputer system may want to control use of that information. !hen several separateprocesses execute concurrently, it should not e possile for one process to interferewith the others or with the operating system itself. 2rotection involves ensuring that allaccess to system resources is controlled. Security of the system from outsiders is alsoimportant. Such security starts with reuiring each user to authenticate himself or herself to the system, usually y means of a password, to gain access to system resources. Itextends to defending external I+" devices, including modems and network adapters,from invalid access attempts and to recording all such connections for detection of reak$ins. If a system is to e protected and secure, precautions must e institutedthroughout it. A chain is only as strong as its weakest link.

1.3.0 ser Operating-System Inter!aceThere are two fundamental approaches for users to interface with the operating system.

"ne techniue is to provide a c$mman%-&ine inter!ace or c$mman% interpreter that allowsusers to directly enter commands that are to e performed y the operating system. The secondapproach allows the user to interface with the operating system via a grap*ica& user inter!aceor 63I.

1.3.0.1 '$mman% Interpreter


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Some operating systems include the command interpreter in the kernel. "thers,such as !indows 72 and 38I7, treat the command interpreter as a special program thatis running when a jo is initiated or when a user first logs on 'on interactive systems(. "nsystems with multiple command interpreters to choose from, the interpreters are knownas s*e&&s. %or example, on 38I7 and 9inux systems, there are several different shells auser may choose from including the Bourne shell , C shell , Bourne-Again shell , the Korn

shell , etc. )ost shells provide similar functionality with only minor differences# mostusers choose a shell ased upon personal preference.

The main function of the command interpreter is to get and execute the nextuser$specified command. )any of the commands given at this level manipulate files:create, delete, list, print, copy, execute, and so on.

1.3.0.0 +rap*ica& ser Inter!ace

A second strategy for interfacing with the operating system is through a user friendly graphical user interface or 63I. 0ather than having users directly enter commands via a command$line interface, a 63I allows provides a mouse$asedwindow$and$menu system as an interface. A63I provides a %est$p metaphor wherethe mouse is moved to position its pointer on images, or ic$ns, on the screen 'the

desktop( that represent programs, files, directories, and system functions. epending onthe mouse pointer4s location, clicking a utton on the mouse can invoke a program,select a file or directory;known as a !$&%er ; or pull down a menu that containscommands.

6raphical user interfaces first appeared due in part to research taking place inthe early ?s at 7erox 2A0- research facility. The first 63I appeared on the 7erox

Alto computer in @. *owever, graphical interfaces ecame more widespread with theadvent of Apple )acintosh computers in the


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error conditions for each operation. !hen the program tries to open the input file, it may findthat there is no file of that name or that the file is protected against access. In these cases, theprogram should print a message on the console 'another seuence of system calls( and thenterminate anormally 'another system call(. If the input file exists, then we must create a newoutput file. !e may find that there is already an output file with the same name. This situationmay cause the program to aort 'a system call(, or we may delete the existing file 'another

system call( and create a new one 'another system call(. Another option, in an interactivesystem, is to ask the user 'via a seuence of system calls to output the prompting message andto read the response from the terminal( whether to replace the existing file or to aort theprogram.

8ow that oth files are set up, we enter a loop that reads from the input file 'a systemcall( and writes to the output file 'another system call(. 1ach read and write must return statusinformation regarding various possile error conditions. "n input, the program may find that theend of the file has een reached or that there was a hardware failure in the read 'such as aparity error(. The write operation may encounter various errors, depending on the output device'no more disk space, printer out of paper, and so on(.

%inally, after the entire file is copied, the program may close oth files 'another systemcall(, write a message to the console or window 'more system calls(, and finally terminate

normally 'the final system call(. As we can see, even simple programs may make heavy use of the operating system. %reuently, systems execute thousands of system calls per second. Thissystem call seuence is shown in %igure elow.

)ost programmers never see this level of detail, however. Typically, applicationdevelopers design programs according to an app&icati$n pr$gramming inter!ace "A,I#. The

A2I specifies a set of functions that are availale to an application programmer, including theparameters that are passed to each function and the return values the programmer can expect.Three of the most common A2Is availale to application programmers are the !in@C A2I for !indows systems, the 2"SI7 A2I for 2"SI7$ased systems 'which includes virtually allversions of 38I7, 9inux, and )ac "S 7(, and the Dava A2I for designing programs that run onthe Dava virtual machine.

%igure


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As an example of a standard A2I, consider the 0ead%ile'( function in the !in@C A2I;afunction for reading from a file. The A2I for this function appears in %igure elow.

%igure


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%igure


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transfer status information

attach or detach remote devices

1.3.5 Fi&e Management

!e can, identify several common system calls dealing with files, we first need to e aleto create and delete files. 1ither system call reuires the name of the file and perhaps some of the file4s attriutes. "nce the file is created, we need to open it and to use it. !e may also read,write, or reposition 'rewinding or skipping to the end of the file, for example(. %inally, we need toclose the file, indicating that we are no longer using it.

!e may need these same sets of operations for directories if we have a directorystructure for organizing files in the file system. In addition, for either files or directories, we needto e ale to determine the values of various attriutes and perhaps to reset them if necessary.%ile attriutes include the file name, a file type, protection codes, accounting information, and soon. At least two system calls, get file attriute and set file attriute, are reuired for this function.Some operating systems provide many more calls, such as calls for file move and copy. "thersmight provide an A2I that performs those operations using code and other system calls, andothers might just provide system programs to perform those tasks. If the system programs arecallale y other programs, then each can e considered an A2I y other system programs.

1.3.5.1 evice Management

A process may need several resources to execute;main memory, disk drives, access tofiles, and so on. If the resources are availale, they can e granted, and control can e returnedto the user process. "therwise, the process will have to wait until sufficient resources areavailale.

The various resources controlled y the operating system can e thought of as devices.Some of these devices are physical devices 'for example, tapes(, while others can e thought of as astract or virtual devices 'for example, files(. If there are multiple users of the system, thesystem may reuire us to first reuest the device, to ensure exclusive use of it. After we arefinished with the device, we release it. These functions are similar to the open and close systemcalls for files. "ther operating systems allow unmanaged access to devices.

"nce the device has een reuested 'and allocated to us(, we can read, write, and'possily( reposition the device, just as we can with files. In fact, the similarity etween I+"devices and files is so great that many operating systems, including 38I7, merge the two into acomined fileEdevice structure. In this case, a set of system calls is used on files and devices.Sometimes, I+" devices are identified y special file names, directory placement, or fileattriutes.

The 3I can also make files and devices appear to e similar, even though the underlyingsystem calls are dissimilar. This is another example of the many design decisions that go intouilding an operating system and user interface.

1.3.5.0 In!$rmati$n Maintenance

)any system calls exist simply for the purpose of transferring information etween theuser program and the operating system. %or example, most systems have a system call toreturn the current time and date. "ther system calls may return information aout the system,such as the numer of current users, the version numer of the operating system, the amount of free memory or disk space, and so on.

In addition, the operating system keeps information aout all its processes, and systemcalls are used to access this information. 6enerally, calls are also used to reset the processinformation.


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1.3.5.3 '$mmunicati$n

There are two common models of inter process communication: the message passingmodel and the shared$memory model. In the message-passing m$%e&, the communicatingprocesses exchange messages with one another to transfer information. )essages can eexchanged etween the processes either directly or indirectly through a common mailox.

5efore communication can take place, a connection must e opened. The name of the other communicator must e known, e it another process on the same system or a process onanother computer connected y a communications network. 1ach computer in a network has ahost name y which it is commonly known. A host also has a network identifier, such as an I2address. Similarly, each process has a process name, and this name is translated into anidentifier y which the operating system can refer to the process. The get hostid and getprocessed system calls do this translation. The identifiers are then passed to the generalpurpose open and close calls provided y the file system or to specific open connection andclose connection system calls, depending on the system4s model of communication. Therecipient process usually must give its permission for communication to take place with anaccept connection call. )ost processes that will e receiving connections are special$purposedaemons, which are systems programs provided for that purpose. They execute a wait for

connection call and are awakened when a connection is made. The source of thecommunication, known as the client, and the receiving daemon, known as a server, thenexchange messages y using read message and write message system calls. The closeconnection call terminates the communication.

In the s*are%-mem$ry m$%e&, processes use shared memories create and sharedmemories attach system calls to create and gain access to regions of memory owned y other processes. 0ecall that, normally, the operating system tries to prevent one process fromaccessing another process4s memory. Shared memory reuires that two or more processesagree to remove this restriction. They can then exchange information y reading and writingdata in the shared areas. The form of the data and the location are determined y the processesand are not under the operating system4s control. The processes are also responsile for ensuring that they are not writing to the same location simultaneously.

5oth of the models just discussed are common in operating systems, and most systemsimplement oth. )essage passing is useful for exchanging smaller amounts of data, ecauseno conflicts need e avoided. It is also easier to implement than is shared memory for inter computer communication. Shared memory allows maximum speed and convenience of communication, since it can e done at memory speeds when it takes place within a computer.

1.3.6 System ,r$grams

Another aspect of a modern system is the collection of system programs. They can edivided into these categories:

& Fi&e management. These programs create, delete, copy, rename, print, dump, list,and generally manipulate files and directories.

& Status in!$rmati$n. Some programs simply ask the system for the date, time,amount of availale memory or disk space, numer of users, or similar statusinformation. "thers are more complex, providing detailed performance, logging, anddeugging information. Typically, these programs format and print the output to theterminal or other output devices or files or display it in a window of the 63I.

& Fi&e m$%i!icati$n. Several text editors may e availale to create and modify thecontent of files stored on disk or other storage devices. There may also e specialcommands to search contents of files or perform transformations of the text.


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& ,r$gramming-&anguage supp$rt. -ompilers, assemlers, deuggers andinterpreters for common programming languages 'such as -, -BB, Dava, /isual5asic, and 2109( are often provided to the user with the operating system.

& ,r$gram &$a%ing an% eecuti$n. "nce a program is assemled or compiled, itmust e loaded into memory to e executed. The system may provide asoluteloaders, relocatale loaders, linkage editors, and overlay loaders. eugging

systems for either higher$level languages or machine language are needed as well.& '$mmunicati$ns. These programs provide the mechanism for creating virtual

connections among processes, users, and computer systems. They allow users tosend messages to one another4s screens, to rowse we pages, to send electronic$mail messages, to log in remotely, or to transfer files from one machine to another.

In addition to systems programs, most operating systems are supplied with programsthat are useful in solving common prolems or performing common operations. Such programsinclude we rowsers, word processors and text formatters, spreadsheets, dataase systems,compilers, plotting and statistical$analysis packages, and games. These programs are known assystem uti&ities or app&icati$n pr$grams.

(O0 an% 3. Insta&& e7uipment%evice system an% '$n%uct testing

INFORMATION SHEET 0.1Sa!ety pr$ce%ures

8arning9 It is essential that you consider closely and follow these recommendations eforeworking on your machine. %ailing to do so can lead to data loss, serious damage to the 2-,personal injury, or even death. eath from a mistake while working on your 2-F ItGs very rare

and easily avoidale if you follow these simple precautions, ut the potential does exist due tothe high voltages present in some 2- components.

+enera& 8arnings

2lease employ common sense in using the material. There are millions of different 2-sout there and no two are exactly alike, so oviously you may run into recommendations or ideasthat donGt apply to your situation. If this happens, use your own good judgment, and then modifythem to suit using your own particulars. If anything stated here conflicts with the specificdirections in your system or component manuals, use the directions in the manual unless youknow them to e inaccurate. onGt go inside the ox or do other work on your 2- if you donGtfeel comfortale with what you are doing.

Is your 2- under warrantyF Hou should realize that some companies will void your warranty if you open the 2- during the warranty period. If you go to open the ox and see anyplastic seals stating warranty void if roken, then that is a good hint that this applies to you utit may even if you donGt see any. If you are having troule with your 2-, check your warranty if you suspect your machine may still e covered. If it is, you may e etter off performing a returnor using your warranty.

E&ectrica& ,recauti$ns


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,u&& t*e p&ug. o not work on a system, under any circumstances, while it is pluggedin. onGt just turn it off and think thatGs enough. "thers have done this and fried things 'or themselvesJ( y accidentally turning the system on while working. Also, the wires that run fromthe power supply to the switch at the front of the ox on an AT form factor system carry livevoltage when the 2- is plugged in, even when it is off. Hou could end up in the hospital over theslip of a screwdriver.

Stay out of the power supply unless you know what you are doing. Similarly, do not openup your monitor unless you are asolutely sure of what you are doing. Hou can electrocuteyourself even with the power disconnected when inside the monitor. There are componentsinside monitors that can hold a charge for a long time after they have een unplugged.

!atch out for components eing left inside the ox. ropping a screw inside your casecan e a hazard if it isnGt removed efore the power is applied, ecause it can causecomponents to short$circuit.

Mec*anica& ,recauti$ns

)ake sure you have a large, flat area to work on. That will minimize the chance of components falling, getting ent, or getting lost.

onGt tighten screws too far or you may strip them or make it impossile to loosen themlater. onGt use screws longer than around


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to ground yourself is to touch the exterior metal ox of your computerGs power supply 'near thefan( efore you unplug it.

8arning9 If you are going to use a grounding strap, uy one, donGt try to make your own ysimply running a wire from your wrist or whatnot. -ommercial grounding straps are speciallydesigned to incorporate a large resistor that protects you in the event that you touch live power

while grounded. !ithout it, you risk ecoming the path of least resistance for that live power toground, and you may e electrocuted.

In general, handle all components y the edges. If you avoid touching any pins,edges, chips, or anything else made of metal, you greatly decrease the chances that you

will zap or reak anything. Smaller components such as loose 0A) chips and processors are atthe greatest risk.

!henever possile, leave static$sensitive devices in their original packaging. Transportcircuit oards and peripherals in an anti$static metallized ag if you do not have the originalpackaging material. *owever, do not put this material inside your 2-, or plug in a motheroardwhile it is sitting on top of one of these ags. They are anti$static ecause they are partiallyconductive# you donGt want your motheroard shorted out y firing it up while several hundredpins from its components are touching a partially conductive material.

Sa!ety 8it* '*i&%ren

If you have children, e extra careful leaving an open machine lying around. Also never leave a 2- running with the cover off. Kids are inuisitive and curiosity and live electricaleuipment donGt mix too well. Kids also like doing cute things like pushing reset uttons andtrying to stick floppy disks into your -$0") drive.

In general, kids should always e supervised when using a 2-. This can help avoid othpossile prolems: the 2- hurting the kids, or the kids damaging the 2- 'or destroying data.(

:acups an% isaster Rec$very

• A )ental 1xercise To 3nderscore the Importance of 5ackups

• The 0isks To Hour ata• 5ackup )ethods, evices and )edia

• 5ackup Scheduling and )edia 0otation Systems

• !hat To 5ack 3p

• *ow To 5ack 3p

• 5oot isks

• isaster 0ecovery

;8*at< me =$rry>; -- A&!re% E. Neuman

8o matter how well you treat your system, no matter how much care you take, youcannot guarantee that your data will e safe if it exists in only one place. The risks are much

greater than most people realize.*ow important is your data to youF Hou can respond to this uestion with words, ut the

steps you take to protect your data are the real answer. Troule comes when people lose largeuantities of data$$ecause they have no ackups$$and then they get very upset, talking aouthow important that data wasJ If itGs important, why wasnGt it acked upF If it matters enough toget upset over losing, itGs worth protecting, and ackups are an essential part of data protection.

There are many reasons that people neglect doing ackups:

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• They donGt understand how important they are, ecause they havenGt had a disaster

happen to them 'yet(.

• They donGt know how to do them.

• They forget to do them ecause they donGt have a routine for doing ackups.

• oing the ackup is a time$consuming chore and they canGt e othered.

This section takes a full look at the matter of ackups, and discusses how to do them,how to set up a ackup program, and what to do in the event of a disaster. 2art of the focus ison making ackups easy to do so that you will rememer to ack up regularly without it takingan inordinate amount of time and energy.

A Menta& Eercise T$ n%ersc$re t*e Imp$rtance $! :acups

)ost unfortunately, there are some things that people only take seriously after they haveexperienced personally the pain that results from not taking them seriously. 5ackups definitely

fall into this category. )ost people are relatively nonchalant aout them until disaster strikes$$thereafter, they are much more diligent aout ackups 'ut after the damage is done.(*ereGs a mental exercise that you can do to help you understand how important ackups

are. Take a look at your 2- and think aout what is on it. Think aout your data and your programs. -onsider how much time it took to create the data, and to set up and tweak your 2-so that it works the way you like. 8ow imagine that one morning you go to your desk and the 2-has vanished without a trace. !hat will you doF

9etGs suppose you had insurance on the hardware, and a week later a new 2- shows upat your door with a fresh new, clean hard disk. 8ow whatF )ost people who ask themselves thisuestion seriously, egin to take ackups much more seriously. '%ortunately, for most peoplethe exercise is only a mental exercise, ut donGt think it canGt happen to you in the real world.(

0ecovering from a disaster such as a total disk crash or theft of a 2- ox can e a very

traumatic event, much more than most 2- users realize. This is true even if ackups exist#when they donGt exist the situation is much, much worse. The pain of recovering from a disaster is almost always very high, and the cost is primarily in the time reuired to recreate the lostdata. %or even a small usiness, this can run into the thousands of dollars very uickly.

T*e Riss T$ ?$ur ata

If you do any sort of reasonale amount of computing, it is only a matter of time eforeyou some day need access to ackups of your data or programs. There are many different risksto your data# most people just think of the infamous, dreaded disk crash. This is a real risk dueto the technology used in data storage, ut there are many other ways that you can easily losedata on your 2-.

:acup Sc*e%u&ing an% Me%ia R$tati$n Systems

In order to provide maximum safety for your data, it is important to plan out a ackupschedule that will allow you the most flexiility and reliaility in recovering from potentialdisasters. This means, in almost every case, the use of multiple ackup media and a ackupschedule that dictates when each set of media should e used. The amount of media neededdepends on how safe you want to e, and what sort of retention period you are looking tomaintain for your data. This section takes a look at scheduling ackups and setting up a mediarotation system, including providing several sample media rotation systems that providedifferent levels of protection 'at appropriate levels of cost(.

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:acup Met*$%s< evices an% Me%ia• )edia Size )atching

• %loppy isks

• 0emovale Storage rives

• 0emovale *ard isks

• In$2lace *ard isk uplication

• 8etwork 5ackup

:acup Met*$%s< evices an% Me%ia

There are many different methods that you can use to ack up the data on your harddisk. The primary difference etween these methods is the device and medium that is used tostore the ackup. ifferent media have different characteristics, such as capacity, speed, ease$of$use, universality, etc.

Me%ia Si@e Matc*ing

"ne very, very important factor to consider when looking at ackup alternatives, ismatching the size of the ackup medium to the amount of data you need to ackup. As harddisks continue to increase greatly in size, it ecomes more difficult to find ackup solutions thatcan handle the entire contents of a 2- using a reasonale amount of media. It is essential thatthe size of the ackup medium e matched to the size of the data eing acked up.

F&$ppy iss

%loppy disks are not suitale as ackup devices for a modern 2-. %loppies are slow,relatively unreliale, and far too small to make effective ackup devices in the age of < 65 harddisks. Their only possile use for ackup is for archiving small files.

%loppy disks are most importantly used as a vehicle for storing critical information aout

your system, for use in the event of a system prolem. These emergency oot disks are eststored on floppies so they can e used in the event of a hard disk prolem.

Rem$va)&e St$rage rives

In the last few years, a whole new class of storage devices has sprung up and ecomevery popular$$removale storage drives. !hile these have existed in various forms for manyyears, it is only recently that they have taken the market y storm. Their popularity rests in their aility to provide removale storage at a reasonale price and with good performance. )any of these drives are also very suitale to use for ackups.

There are so many different drives, and they differ in so many different. 9ooking at thevarious characteristics of these drives, we see that many of them are suitale for ackup

purposes, ut some really are not. The drives fall into several categories:

• (arge F&$ppy is E7uiva&ent rives9 These devices are suitale for ackuponly if you have a small hard disk, or have the diligence and patience to do attendedackups or large numers of partial ackups. As hard disks increase in size to L 65and eyond, trying to do ackups to a device that is only a little more than


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• Rem$va)&e Har% is E7uiva&ent rives9 These are much more suitale for useas ackup devices due to their larger capacity, ut even here things are ecomingstretched, since even M?? )5 to < 65 is ecoming inadeuate for unattendedackups. These drives have generally much higher performance than the smaller drives, and much higher price tags to go with them.

• '-Rec$r%a)&e9 These are write$once read$many drives with a capacity of aoutNM? )5. The capacity is on the small side at NM? )5. "ne great advantage is thatthe ackups are readale y any -$0") drive.

• '-Re=ritea)&e9 This drive is really in the same category as the removale hard

disk euivalents listed aove. -$0! has a lot going for it as a general-purposemedium, ecause of its flexiility: its media are reusale and it can also urn -$0sthat play in most -$0")s or audio -s as well. The capacity is only NM? )5.

In-,&ace Har% is up&icati$n

"ne ackup solution that some people who have more than one hard disk use is to setup their system so that they use one hard disk for their programs and data, and the other one asa ackup. They then copy the contents of the one hard disk to the other on a regular asis,using a file$ or disk$copy tool.

This scheme is interesting and can e useful in some ways, although it has some severelimitations as well. Its advantages are that it is simple, and that it is automatale# you can set itup to do this on a nightly asis and know that everything on your hard disk will e duplicatedautomatically without you having to rememer to do anything. This increases the chances thatthe ackup will e done. The performance of the disk$to$disk copy will e very high, and the costis pretty much reasonale.

The drawacks of this sort of a scheme however are significant. %irst, it doesnGt protectagainst very many of the risks to your data$$it is not going to help much against theft, fire,

saotage, many types of viruses, and even some types of hardware failure. Second, you canonly have a single ackup, which makes the whole system very vulnerale$$if you make a copyof the whole disk every night, what happens if you only notice a prolem three days after itwipes out some of your dataF

Net=$r :acup

The idea is fairly simple: copy data from one 2- to another over the network. uplicatingeach 2-Gs information provides a way to protect each individual 2-.

In a way, this type of ackup is most similar to in$place hard disk duplication in terms of how it works. It is simple in the same way, and can e automated. It addresses some of theconcerns aout that method: there isnGt the same single point of failure in terms of virus attack

or hardware failure. *owever, depending on the location of the two 2-s, theft, disaster andsaotage can still e a ig prolem: if the two 2-s are sitting on different desks in the sameoffice, you havenGt gained much to protect against these threats. Also rememer that file$infector viruses can travel over a network.

'$mparis$n $! :acup Met*$% ata Ris '$verage

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Some of the ackup methods and devices descried in this section do a much etter jothan others of protecting against the risks to your data. The tale elow shows a generalsummary of how the various methods stack up in terms of protecting you from the hazards thatthreaten your valuale data. 0ememer that this is just a general guideline# also rememer thatsome of these risks are much more common than others are, depending on how you use your 2-:

'$mparis$n $! :acup Met*$% '*aracteristics

In order to help you understand how the various ackup methods compare to each other and help you make a decision aout which one makes the most sense for you, enclosed thechart elow. It evaluates the various ackup methods in several different important generalareas. These areas are:

• 'apacity9 *ow much does the medium store, relative to current average harddisksF Is it likely that an average userGs hard disk will fit onto one or maye twopieces of media for the device+methodF

• Aut$mata)i&ity9 *ow possile is it to fully automate the ackup so that it happenswithout any user intervention at allF

• Minimi@e% Startup '$st9 *ow well does the method minimize startup costs for hardware or softwareF

• Minimi@e% Me%ia '$st9 oes the method allow additional ackups at a reasonalecostF

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• Epan%a)i&ity9 *ow possile is it to do more ackups, or add additional ackupmedia if neededF

• Re&ia)i&ity9 In general terms$$ecause this varies widely ased on the type of device for items such as tape drives$$how likely is it that if you have a disaster and

need to restore from the ackup, it will work for youF

• Simp&icity '$nvenience9 *ow easy is the method to useF Is there any difficulty

associated with the method that would tend to discourage doing ackupsF

• niversa&ity9 *ow common is the hardware used for the methodF If you needed to

use the device in five years, how likely is it that you could find support or additionalmedia for itF

• ,er!$rmance9 *ow fast is the hardware and software used for the methodF *ow

much time will it take to do a ackupF

• R$utine ,$tentia&9 In general, how likely is it that, using this method, someone is

likely to settle into a ackup routine and stick with itF

*ere is the chart# for all items, *igh is etter and 9ow is worse:


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8*at T$ :ac p

• %ull, Selective and Incremental 5ackups

• 5acking 3p 2rograms and ata

• %iles 8ot to 5ack 3p

• 9ong %ilenames

• %ile System 2arameters• 5I"S Settings '-)"S )emory( 5ackup

8*at T$ :ac p

To ensure that your ackups are performed properly, in a way that ensures that you areprotected without taking so much of your time that they ecome a chore, you must determinewhat files to ack up and how often to ack them up. Some files will need to e acked up more

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often than others. This section takes a look at what files you will want to include in your ackuproutine, and also the ones you will usually want to exclude.

Fu&&< Se&ective an% Incrementa& :acups

There are several different ways that we can select files for ackup. The way that youwill want to use depends on how you use your system, how often your files change, and your

chosen ackup method. )any people will in fact end up using a comination of these differenttechniues:

• Fu&& :acup9 8othing complicated here, a full ackup is done y selecting all thefiles on the hard disk for ackup. "nly special files that should not e acked up atall are left out. This is the simplest type of ackup, and yields the most completeackup image, ut it takes the most time and media space to do.

• Se&ective :acup9 In a selective 'or partial( ackup, you select specific files and

directories to ack up. This type of ackup gives you more control over what isacked up, at the expense of leaving part of the hard disk unprotected. Selectiveackups make sense when some files are changing much more rapidly than others,or when ackup space is limited, although in many cases doing an incrementalackup is etter and easier.

• Incrementa& :acup9 If you perform freuent ackups, as you should, you may

find yourself acking up the same files over and over, even ones that do not changeover time. Instead, you may want to consider a mix of full ackups and incrementalackups. An incremental ackup is one where only the files that have changed sincethe last ackup are selected. It is like a selective ackup, ut the files are selectedased on whether they have changed recently or not, instead of an aritraryselection ased on directory or file names. This gives the time$ and space$savingadvantages of a selective ackup while also ensuring that all changed files arecovered.

Incremental ackups are supported y most decent ackup software. They work usingthe archive it that exists for each file and directory. The ackup software looks at this it todetermine what files have een changed since the last ackup, selects them for ackup, andthen clears the it for all the files it acks up. If any files are changed, the software sets the itagain so on the next incremental they are again selected, and so on. Hou must rely on this iteing managed properly, and I donGt always like to do this.

!hich type of ackup you do depends, again, on what is important to you, in terms of time, media cost, and also ease of restoration.

:acing p ,r$grams an% ata

)ost files on a typical 2- can e roken down, loosely, into eing either programs or data. These differ of course in many ways, ut not least are in how they should e consideredfor ackup.

In general, data files should always e acked up. These are the fruit of your laor, andcannot e replacedJ 1very ackup should include all of your data, either via a full ackup of theentire hard disk, a selective ackup that includes the directories where the data is, or anincremental ackup. '*aving all your data in a handful of directories instead of scattered all over the hard disk is useful, for this very purpose(.

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2rograms are a somewhat different story for two main reasons: first, they are static,meaning once installed they do not change 'with a few exceptions(. Second, they arerecreatale# if your )icrosoft "ffice directory gets wiped out, you can reinstall it from your original -$0") disk. The comination of these characteristics suggests that acking upprograms is less important than acking up data, and this is true. 2rograms do not need to eacked up as often as data does.

N$te9 Some 2-s ship with their software preinstalled on the hard disk and no original disks or -$0")sJ This is a poor practice and I recommend that people avoid uying from companiesthat do this, since it makes it very hard for you to reinstall software if you need it in case of disaster. If you have no original disks, your installed programs should e treated as just as

unrecreatale as your data.

Fi&es N$t t$ :ac p

There are some files that should never e acked up. The main reason is that some filesdo not contain anything that would matter if they were lost. Another reason is that some files arerepresentations of programs or data that are etter acked up in a different form. !hile virtuallyall regular files should e acked up, in most cases the following kinds of files should eexcluded from routine ackups:

• S=ap Fi&es9 A swap file is a large file that is used y the operating system for virtualmemory. !hen the system needs more memory than actually exists in the 2-, itcreates a virtual memory space and applications share the real memory yswapping pieces of memory to the hard disk. The swap file holds these pieces. Thisfile can e uite large, sometimes exceeding M? )5 in size depending on thesystem. Since it does not contain any real data, ut rather is a placeholder for information in memory while the 2- is running, there is no point in acking it up.

• '$mpresse% $&ume Fi&es9 If you use volume$ased disk compression, thecompressed volume that you see mounted as a drive letter is stored on the host disk

as a single file called a compressed volume file or -/%. All the files on thecompressed disk are in this file. If you use compressed volumes, the files on themshould e acked up individually from the compressed volume. The ig -/% file onthe host disk should not e acked up, since it contains the same information ut ina way that is much more difficult to restore.

)ost newer software will in fact automatically deselect the items aove, unless youoverride and tell it you want them included anyway. )any types of ackup software will also letyou select classes of files, y file type, that you want to exclude for whatever reason.

($ng Fi&enames

9ong filenames use special tricks in the directory structure to store names of up to aoutCM? characters while maintaining compatiility with older "S and !indows @.x applicationsthat use standard short filenames..

In terms of ackup, 9%8s present no concern as long as you use a ackup utility thatknows how to deal with them. Hou do have to exercise some caution when moving files etween2-s due to the tendency for the short filename aliases to move around when changing filesetween systems. %or standard ackup of a 2-, long filenames should not pose a prolem if you are using the right software.

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:IOS Settings "'MOS Mem$ry# :acup

There is an essential set of information that is critical to the operation of your 2-, ut isnot stored on your hard disk at all. It is your 5I"S settings, the group of parameters that controlscritical aspects of how your 2- works These settings are very important ecause minor changes to them can have a major impact on how your system functions. It can take a long time

to tweak your 5I"S settings to reach the set that allows your system to function at peakperformance.

The 5I"S settings for your 2- are not stored in the system memory or hard disk.Instead, they are stored in a special reserved memory area that is commonly called the -)"S)emory. A attery provides ackup so that the settings are not lost when the 2- is turned off or unplugged. 3nfortunately, certain situations can cause the -)"S memory to e erased or settings lost# usually this can happen when the attery fails due to some sort of malfunction, or merely ecause the motheroard is getting old.

It makes sense therefore to ack up the information in the -)"S memory on occasion.3nder normal circumstances, the attery will last for uite a while, and most regular 2-s keeptheir 5I"S settings intact for years at a time. This means that the -)"S does not need to eacked up at nearly the freuency that regular data does. In fact, once you have created your

initial ackup 'which you should do when you set up your 2-(, all you need to do is change theackup whenever you change the settings themselves, to make sure the ackup is current.

Since the data is not on the hard disk, you canGt just ack this information up the way youwould a regular file. There are in fact two different ways that the -)"S memory is normallyacked up:

• Manua& :acup9 Take a piece of paper and your favorite writing implement. 6othrough the 5I"S setup screens and record the settings and what their values are. Itsounds tedious, ut it is simple, foolproof O while it takes a while to do the first time, thisis something you only do once when you set up a new 2-, or change the motheroard.!hen you change your 5I"S settings, you just change what is written on the piece of paper as well.

Tip9 It is possile with some 5I"Ses to get the 5I"S setup screens to print out on the printer.Turn on the 2-, and oot up "S. Then hit P-trlQBPAltQBPeleteQ to reset the 2-, and go into5I"S setup. "n some systems, the routine that handles the P2rint ScreenQ key will still function,

and you can use it on each of the 5I"S screens as a nifty shortcutJ

• 'MOS :acup ti&ities9 There are small utilities that will go through the -)"Ssettings and record them to a regular file, which can then e acked up through

normal means, or just copied to a couple of floppy disks. Some of these programsalso offer the option of restoring the -)"S settings from one of these files if the-)"S ever gets wiped out.

H$= T$ :ac p

• 5ackup Timing

• 5ackup Software

• Software -onflicts

• ata /erification

• 5ackup -ompression

• )edia Storage

!hile acking up your data is in some ways a simple matter there are in fact somespecial techniues that can come into play to make ackups more effective and less of a

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hassle. This section takes a look at specific techniues and considerations for performingackups, some of which you might not think of. This includes a discussion of ackup timing,scheduling, media storage, O how to ensure that your ackups work, O will protect you in theevent that you need them.

:acup Timing

Selecting a time of day to perform ackups is a matter of personal choice. It depends, asusual, on how you use your 2-, and also on how long it takes for you to perform ackups. )ostpeople prefer to do unattended ackups, and therefore, set their ackups up to run when theyare not around. The most common times to run ackups therefore are:

• Overnig*t9 start a ackup efore going to sleep, have it run overnight, and then see

the results in the morning. This makes sense ecause the 2- isnGt eing used, and afull ackup of a loaded system, including time to perform verification, can takeseveral hours.

• uring t*e ay9 If you work during the day you can set up your home machine to

perform ackups while you are at the office. This is really not much different inconcept from the overnight ackup# oth use slack time where the 2- isnGt eingactively used, to perform ackups.

:acup S$!t=are

An important part of the ackup puzzle is using the right software. The differenceetween good and mediocre ackup software can e the difference etween ackups that arereliale and easy to use and ones that are not. The difference etween mediocre software andad software can e the difference etween ackups that restore properly when you need themto, and those that leave you high and dryJ

)any ackup devices ship with asic ackup software, provided as a courtesy y the

hardware manufacturer. In many cases these are functional ut stripped$down versions of commercial packages. They will usually work, ut may not e nearly as full$featured as apackage you would uy at the store. The following are ailities or features that you may want toconsider carefully when looking at 2- ackup software 'not listed in any particular order(:

• 8i%e evice Supp$rt9 5ackup software varies significantly in its aility to support

ackup devices. 6enerally speaking, it is more difficult to find software support for newer devices than well$estalished ones. Some software companies will makesoftware updates availale for their users to provide expanded support as new driveshit the market# others will not. o rememer that while support for more devicesgives you more flexiility, ultimately the only device you really need support for is theone that you are actually using.

• Operating System Supp$rt9 The software should support all of the features andreuirements of the operating system under which it runs. This means, for example,that !indows = software should have full support for long filenames, ackup of the!indows = 0egistry, and ackup of %AT@C partitions.

• :acup Type Se&ecti$n9 All good ackup software will let you choose etween

doing full, selective and incremental ackups. 5etter ones will let you select files anddirectories ased on search strings or patterns.

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• Me%ia Spanning9 The software should provide proper support for acking up to

multiple pieces of media in a media set. So if you did a ackup to Rip disks and thedata took up CM? )5, the system should prompt you when it is time to switch disks,

etc. Strangely, some poor ackup software has prolems with this.

•isaster Rec$very9 A very important feature, and one that is often found only onmore expensive products is support for automatic disaster recovery. !ith this type of software, sometimes called one-step recovery or single-step restore or similar, afloppy disk is created with a special recovery program that will let you restore your system simply. !ithout this feature, you often have to reinstall the entire operatingsystem efore you do a restore, which can cost a lot of time and cause a lot of

prolems.

• Sc*e%u&ing an% Aut$matic Operati$n9 epending on how and when you do your

ackups, it can e very helpful to have the software run automatically at a presettime.

• :acup eri!icati$n9 1very decent ackup package will allow you to enale a

verification mode. !hen active, the software will read ack from the tape every filethat it acks up and compare it to the file on the hard disk, to ensure that the ackupis correct. This is important to ensure that your ackups are viale.

• '$mpressi$n9 6ood ackup software will give you the option of enaling software

compression, possily at various levels, to enale you to save space on your ackupmedia.

• Security9 5etter software packages will let you password$protect a ackup set so

that the password is reuired to view or restore from the ackup image. '5e verycareful efore using something like this, you donGt want to lose that passwordJ(

S$!t=are '$n!&icts

!hen performing ackups in a multitasking operating system, it is necessary to e waryof possile conflicts etween the ackup software and any other software that may e runningsimultaneously. Any programs that are running in the ackground that might write to files or directories on the disk can confuse the ackup software, especially when it goes to verify thefiles it has acked up, ecause it may find different files in some directories at the end of theackup compared to what was there at the eginning.

Another prolem is with files that are locked due to another program having exclusive

access to the file. To prevent more than one application from changing a document at the sametime, many applications will lock them out so no other application can use them. This can causethe ackup software to e unale to ack up these files.

The solution to avoiding these prolems is, in most cases, to simply turn off other software when you are doing a ackup. isale your screen saver, to ensure that it doesnGtcause interference.

ata eri!icati$n

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The idea ehind verification is simple: after the files are acked up, the ackup softwarereads ack the information from the ackup media and compares it ack to the original files.This ensures that the ackup just made is readale, and that the files match what was justcopied. The only disadvantage is that it lengthens the amount of time that it takes to perform theackup, ut if you are acking up overnight or while away from the 2-, this will have no effecton you anyway.

There are two different levels of verification that you will sometimes find, depending onthe software you are using. The most secure level of verification is full verification, where eachand every file that is acked up is also verified y reading ack from the ackup medium. Alesser type of verification is sampling verification. *ere, instead of verifying everything that wasacked up, a sample of what was acked up is read ack and verified. This makes theverification take much less time, ut of course doesnGt do nearly as good a jo.

:acup '$mpressi$n

)ost ackup systems support some type of compression. The idea ehind compressionis simple: to save space and allow the ackup of more data onto a given media set. )ostsoftware supports compression, and in fact many ackup devices even uote their capacity on

the assumption that compression will e used during ackup.8ormally there is nothing wrong with using compression, and in fact I use it myself in

many cases. Hou do need to ear in mind a few things, however:

• '$mpressi)i&ity9 8ot all files will compress eually well. If you are acking up a

large numer of files that are already in a compressed format, it may make sense toturn off compression, since it isnGt going to do much for you anyway.

• ,r$prietary F$rmats9 1ach software program will use its own compression

algorithm. This means that the tape written y one program may not e readale ya different software package. This is not normally a prolem since most people onlyuse one package on one 2-, ut it is something to ear in mind. The ackup formats

themselves are reasonaly universal if compression is not used.Me%ia St$rage

• Hour data ackups are exactly as safe as the physical media that contains them. If you

do a tape ackup and then leave the tape lying on top of the 2- ox, then you arepartially defeating the purpose of doing ackups. Hou will give ack the protection thattape offers against risks like theft, disaster or saotage.

• 5ackup media should e stored in a safe place, away from the 2-.

• epending on the type of ackup media you are using, you want to make sure that the

storage environment is appropriate. %or magnetic media such as tapes and disks, youwant to ensure that the storage area offers protection from the hazards that threatenthem, including temperature, moisture, dirt, magnetic fields and the like.

• %inally, pay attention to the matter of off$site storage. It is a good idea to ensure that one

or more of the ackup media sets in the media rotation system you are using is alwayse stored off$site. This is important to allow for safeguarding against total disaster likehurricane.

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