Lenovo ThinkServer - About RAID

•“ConguringRAIDusingtheThinkServerEasyStartupprogram”onpage74
•“ConguringtheonboardSATAsoftwareRAID”onpage75
•“ConguringtheadvancedSATAorSAShardwareRAID”onpage80
AboutRAID
RAID,anacronymforRedundantArrayofIndependentDisks,isatechnologythatprovidesincreased
storagefunctionsandreliabilitythroughredundancy.Thisisachievedbycombiningmultipleharddiskdrives
intoalogicalunit,wheredataisdistributedacrossthedrivesinoneofseveralwayscalledRAIDlevels.
WhenagroupofindependentphysicalharddiskdrivesaresetuptouseRAIDtechnology,theyareina
RAIDarray.Thisarraydistributesdataacrossmultipleharddiskdrives,butthearrayappearstothehost
serverasonesinglestorageunit.CreatingandusingRAIDarraysprovideshighperformance,suchasthe
expeditedI/Operformance,becauseseveraldrivescanbeaccessedsimultaneously.
RAIDdrivegroupsalsoimprovedatastoragereliabilityandfaulttolerancecomparedtosingle-drivestorage
systems.Datalossresultingfromadrivefailurecanbepreventedbyreconstructingmissingdatafromthe
remainingdrives.
ThefollowinglistdescribessomeofthemostcommonlyusedRAIDlevels:
•RAID0:block-levelstripingwithoutparityormirroring
SimplestripesetsarenormallyreferredtoasRAID0.RAID0usesstripingtoprovidehighdata
throughput,especiallyforlargelesinanenvironmentthatdoesnotrequirefaulttolerance.RAID0hasno
redundancyanditprovidesimprovedperformanceandadditionalstoragewithoutfaulttolerance.Any
drivefailuredestroysthearrayandthelikelihoodoffailureincreaseswithmoredrivesinthearray.RAID
0doesnotimplementerrorchecking,soanyerrorisuncorrectable.Moredrivesinthearraymeans
higherbandwidth,butgreaterriskofdataloss.
RAID0requiresaminimumnumberoftwoharddiskdrives.
•RAID1:mirroringwithoutparityorstriping
RAID1usesmirroringsothatdatawrittentoonedriveissimultaneouslywrittentoanotherdrive.Thisis
goodforsmalldatabasesorotherapplicationsthatrequiresmallcapacitybutcompletedataredundancy.
RAID1providesfaulttolerancefromdiskerrorsorfailuresandcontinuestooperateaslongasatleast
onedriveinthemirroredsetisfunctioning.Withappropriateoperatingsystemsupport,therecanbe
increasedreadperformanceandonlyaminimalwriteperformancereduction.
RAID1requiresaminimumnumberoftwoharddiskdrives.
•RAID5:block-levelstripingwithdistributedparity
RAID5usesdiskstripingandparitydataacrossalldrives(distributedparity)toprovidehighdata
throughput,especiallyforsmallrandomaccess.RAID5distributesparityalongwiththedataandrequires
alldrivesbutonetobepresenttooperate;drivefailurerequiresreplacement,butthearrayisnot
destroyedbyasingledrivefailure.Upondrivefailure,anysubsequentreadoperationscanbecalculated
fromthedistributedparitysothatthedrivefailureismaskedfromtheenduser.Thearraywillhavedata
lossintheeventofaseconddrivefailureandisvulnerableuntilthedatathatwasonthefailingdriveis
rebuiltontoareplacementdrive.Asingledrivefailureinthesetwillresultinreducedperformanceof
theentiresetuntilthefailingdrivehasbeenreplacedandrebuilt.
RAID5requiresaminimumnumberofthreeharddiskdrives.
72ThinkServerUserGuide