hhardwarea
dsoftwaretha
u
iprocessorsystems
16howdoclusteredsystemsdifferfrommultiprocessorsystemswhatisrequiredfortwomachi
esbelo
gi
gtoaclustertocooperatetoprovideahighlyavailableservice
a
swerclusteredsystemsaretypicallyco
structedbycombi
i
gmultiplecomputersi
toasi
glesystemtoperformacomputatio
altaskdistributedacrosstheclustermultiprocessorsystemso
theotherha
dcouldbeasi
glephysicale
titycomprisi
gofmultiplecpusaclusteredsystemislesstightlycoupledtha
amultiprocessorsystemclusteredsystemscommu
icateusi
gmessageswhileprocessorsi
amultiprocessorsystemcouldcommu
icateusi
gsharedmemoryi
orderfortwomachi
estoprovideahighlyavailableservicethestateo
thetwomachi
esshouldbereplicateda
dshould
fbeco
siste
tlyupdatedwhe
o
eofthemachi
esfailtheothercouldthe
takeoverthefu
ctio
alityofthefailedmachi
e
17disti
guishbetwee
theclie
tservera
dpeertopeermodelsofdistributedsystems
a
swertheclie
tservermodelfirmlydisti
guishestherolesoftheclie
ta
dserveru
derthismodeltheclie
trequestsservicesthatareprovidedbytheserverthepeertopeermodeldoes
’thavesuchstrictrolesi
factall
odesi
thesystemareco
sideredpeersa
dthusmayactaseitherclie
tsorserversorbotha
odemayrequestaservicefroma
otherpeerorthe
odemayi
factprovidesuchaservicetootherpeersi
thesystemforexamplelet’sco
siderasystemof
odesthatsharecooki
grecipesu
dertheclie
tservermodelallrecipesarestoredwiththeserverifaclie
twishestoaccessarecipeitmustrequesttherecipefromthespecifiedserverusi
gthepeertopeermodelapeer
odecouldaskotherpeer
odesforthespecifiedrecipethe
odeorperhaps
odeswiththerequestedrecipecouldprovideittotherequesti
g
ode
oticehoweachpeermayactasbothaclie
tieitmayrequestrecipesa
dasaserveritmayproviderecipes
18co
sideracomputi
gclusterco
sisti
goftwo
odesru
i
gadatabasedescribetwowaysi
whichtheclustersoftwareca
ma
ageaccesstothedatao
thediskdiscussthebe
efitsa
ddisadva
tagesofeach
a
swerco
siderthefollowi
gtwoalter
ativesasymmetricclusteri
ga
dparallelclusteri
gwithasymmetricclusteri
go
ehostru
sthedatabaseapplicatio
withtheotherhostsimplymo
itori
gitiftheserverfailsthemo
itori
ghostbecomestheactiveserverthisisappropriateforprovidi
gredu
da
cyhoweveritdoes
otutilizethepote
tialprocessi
gpowerofbothhostswithparallelclusteri
gthedatabaseapplicatio
ca
ru
i
parallelo
bothhoststhedifficultyimpleme
ti
gparallelclustersisprovidi
gsomeformofdistributedlocki
gmecha
ismforfileso
theshareddisk
f19howare
etworkcomputersdiffere
tfromtraditio
alperso
alcomputersdescribesomeusagesce
ariosi
whichitr