Specifications

Storage Subsystem Guide

4 System Drives and System Drive

Groups

System Drives

Logically,systemdrives(SDs)arethebasicstorageelementusedbythe

storageserver.Theserverassignseachsystemdriveauniqueidentifying

number(ID)and,onceassigned,theSDisreferencedbythatIDnumber,and

theIDnumbermaynotbechanged.

Physically,eachSDismadeupof

severalphysicaldisks.Thesizeofthe

systemdrivedependsonfactorssuchastheRAIDlevel,thenumberofdisks,

andtheircapacity.SeeSupportedStorageSubsystems,onpage11for

informationontheRAIDlevel(s)supportedbyyourstoragesubsystem(s).

OnallIS‐NASServer/clusters,andallSeries

3000TitanServers/clusters,

systemdrivescanbeorganizedintosystemdrivegroups,whichcanimprove

theperformanceofastorageserverorclusterbyoptimizingreadsandwrites.

System Drive

Groups

Withmanystoragesubsystems,systemdrives(SDs)arelimitedto2TB

each.However,withtodayʹslargephysicaldisks,RAIDarraysmustbe

considerablylargerthan2TBinordertomakeefficientuseofspace.Soitis

commonforsystemadministratorstobuildlargeRAIDarrays(oftencalled

ʺRAID

groupsʺorʺvolumegroupsʺ)andthendividethemintosystemdrives

(SDs)of2TBorless.NotethateachSDinaRAIDgrouptypicallyusessome

spaceoneachdiskintheRAIDgroup.SDsaretheunitsofstoragethatthe

serverseesandmanages(theserverorganizes

SDsintoStoragePools,which

thencontainthefilesystems).

Whenperformingwriteoperations,iftheserverweretowritesimultaneously

tomultipleSDsinthesameRAIDgroup,itwouldincreasehead‐movement,

reducingbothperformanceandtheexpectedlifeofthedisks.Sotheserver

hasamechanismto

allowittowritetoonlyoneSD(LUN)inaRAIDgroupat

anyonetime.BydefiningSDgroups, youtelltheserverwhichSDsareineach

RAIDgroupandgiveittheinformationitneedstooptimizewrite

performance.

Note:ForTitanServer/clusters,systemdrivegroupsare

supportedonSeries

2000andSeries3000storag eservers,butonlySeries3000TitanServers/clusters

takeadvantageofthisfunctionality.AllIS‐NASServers/clu sterstake

advantageofsystemdrivegroups.

Asystemdrivethatisnotinanygroupistreatedasifitwereinagroupofits

own.