lec11-storage-raid.ppt

8/9/2019 lec11-storage-raid.ppt

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Lecture 11: Storage SystemsDisk, RAID, Dependability

Kai [email protected]

http://list.zju.edu.cn/kaibu/comparch


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Appendi! D"1#D"3


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1$%&s # 1$'&s

(omputing Re)olution


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1$$& #

In*ormation Age


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(ommunication(omputation

Storage


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Storage


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Storagerequires higher standard ofdependability than the rest of the computer


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program crash


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data loss


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(ommunication

Storagemagnetic disks dominate


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+utline

iskisk 3rray: R34

ependability: 5ault6 7rror6 5ailure


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+utline

iskisk 3rray: R34



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Disk

http://c8.ydcdn.net/ .0. . &/ima(es/computer/M39 4 K.945


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Disk

http://%%%.cs.uic.edu/;jbell/peratin( ystems/ima(es/


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Disk (apacity

Areal Density*bits/inch 2

* tracks/inchA bitsCperCtrack/inchA


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Disk (apacity

Areal Densityin 20 6 the hi(hest density

-00 billion bits per sDuare inch(osts per gigabytebet%een &' and 20 6

improEed by almosta 8actor o8 60006000


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Disk *or Secondary Storage

Cost DRAM >> DISK

Access time DRAM


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Disk s (ompetitor

-las .emorynonCEolatile semiconductor memoryF

same band%idth as disksF00 to 000 times 8asterF to 2 times hi(her cost/(i(abyteF

/ear outlimited to million %ritesPopular in cell p ones,

but not in desktop and ser)er


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Disk Po0er

Po0er by disk motoriameter -.+ R#M 2.' =o. o8 platters

R#M: ReEolutions #er Minute rotation speed maller patters6 slo%er rotation6 and

8e%er platters reduce disk motor po%er


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Disk Po0er


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+utline

iskisk 3rray: R34



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Disk Arrays

isk arrays %ith redundant disks totolerate 8aults48 a sin(le disk 8ails6 the lostin8ormation is reconstructed 8romredundant in8ormationStriping : simply spreadin( data oEermultiple disksRAID: redundant array o8ine pensiEe/independent disks


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RAID


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RAID &

2 +D: just a bunch o8 disks=o redundancy

=o 8ailure toleratedMeasurin( stick 8or other R34 leEels interms o8 cost6 per8ormance6 and

dependability


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RAID 1

.irroring or S ado0ingG%o copies 8or eEery piece o8 dataone lo(ical %rite * t%o physical %rites

00H capacity/spaceoEerhead

http://%%%.petemaroEichima(es.com/%pCcontent/uploads/20 / /R34 .jp(


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https://%%%.iccCusa.com/content/raidCcalculator/raidC0C .pn(


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RAID

http://%%%.acnc.com/raidedu/27ach bit o8 data %ord is %ritten to a data diskdriEe

7ach data %ord has its "ammin(


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RAID 3

http://%%%.acnc.com/raidedu/ata striped oEer all data disks

#arity o8 a stripe to parity diskReDuire at least disks to implement


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P

10100011

11001101

10100011

11001101

RAID 3

7Een #arityparity bit makes

the 1 o8 eEenp * sum data A mod 2RecoEery

i8 a disk 8ails6 IsubtractJ (ood data8rom (ood blocksF

%hat remains is missin( dataF


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RAID 4

http://%%%.acnc.com/raidedu/-5aEor small accesses

3llo%s each disk to per8ormindependent reads6 usin( sectors o%nerror checkin(


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RAID 5

http://%%%.acnc.com/raidedu/istributes the parity in8o across all

disks in the arrayRemoEes the bottleneck o8 a sin(leparity disk as R34 and R34 -


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RAID %: Ro06diagonal Parity

RAID6DPRecoEer 8rom t%o 8ailures

orro%: 00L L22L *r-

dia(onal: 0 L L Lr *d


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Double6-ailure Reco)ery


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RAID: -urt er Readings

Raid Gypes


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+utline

iskisk 3rray: R34



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Ghe ser)ice deliEered by a system isits obserEed actual be a)ior asperceiEed by other system sAinteractin( %ith this system s users.


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7ach module also has an idealspeci*ied be a)ior 6 %here a ser)icespeci*ication is an a(reed descriptiono8 the e pected behaEior.


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-ailure

3 system *ailure occurs %hen theactual behaEior deEiates 8rom thespeci8ied behaEior.


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7rror, -ault

Ghe 8ailure occurred because o8 anerror 6 a de8ect in that module.Ghe cause o8 an error is a *ault .

Ohen a 8ault occurs6 it creates a latenterror 6 %hich becomes e**ecti)e %henit is actiEatedFOhen the error actually a88ects thedeliEered serEice6 a 8ailure occurs.


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-ault, 7rror, -ailure

3 8ault creates one or more latenterrors7ither an e88ectiEe error is a 8ormerlylatent error in that component or it haspropa(ated 8rom another error in thatcomponent or 8rom else %here3 component 8ailure occurs %hen theerror a88ects the deliEered serEice


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(ategories o* -aults by (ause

8ard0are *aults8ailed deEicesDesign *aults

usually in so8t%are desi(nFoccasionally in hard%are desi(nF+peration *aults

mistakes by operations and maintenancepersonnelF7n)ironmental *aults8ire6 8lood6 earthDuake6 po%er 8ailure6

sabota(eF


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(ategories o* -aults by Duration

9ransient *aultse ist 8or a limited time and are notrecurrin(FIntermittent *aultscause a system to oscillate bet%een8aulty and 8aultC8ree operationPermanent *aultsdo not correct themselEes %ith the

passin( o8 timeF

l k l


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7!ample: erkeley s9ertiary Disk


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7!ample: 9andem


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7!ample: 9andem


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lec11-storage-raid.ppt