Specifications

The SGI InfiniteStorage NAS Storage System
10 SGI InfiniteStorage NAS Server and Titan Server
followingillustrationshowsacompletepathfromtheservertoeachofthe
SDsonthestoragesubsystem:
YoucanviewinformationabouttheFCpathsontheserver/clusterthrough
thecommandlineinterface(CLI),usingthe
fc-host-port-load,fc-
target-port-load
,andthesdpathcommands.
Load Balancing
and Failure
Recovery
Loadbalancingonastorageserverisamatterofbalancingtheloadstothe
systemdrives(SDs)onthestoragesubsystems(RAIDarrays)towhichthe
storageserverisconnected.SDsarealogicaldivisionofagroupofthe
physicaldisksofthestoragesubsystem,andtheSDis
thebasicstorageunitof
thestoragesubsystem.
TheserverroutesFCtraffictoindividualSDsoverasingleFCpath,
distributingtheloadacrosstwoFCswitchesand,whenpossible,acrossdual
active/activeormulti‐portRAIDcontrollers.
Followingthefailureofapreferredpath,diskI/Oisredistributed
among
other(non‐preferred)paths.Whentheserverdetectsreactivationofthe
preferredFCpath,itonceagainredistributes diskI/OtousethepreferredFC
path.
Defaultloadbalancing(loadbalancingautomaticallyperformedbythe
storageserver) isperformedbasedonthefollowingcriteria:
•“Load”isdefinedasthenumberof
openSDs,regardlessofthelevelofI/O
oneachSD.SDscounttowardsloadatthetargetiftheyareopentoatleast 
oneclusternode;thenumberofnodes(normallyallnodesinacluster,
afterboot)isnotconsidered.