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Table Of Contents
Getting Started with vSphere Command-Line Interfaces
48 VMware, Inc.
Thetypeofarrayandthepathpolicydeterminethebehaviorofthehost.
Multipathing Considerations
Thefollowingconsiderationshelpyouwithmultipathing:
IfnoSATPisassignedtothedevicebytheclaimrules,thedefaultSATPforiSCSIorFCdevicesis
VMW_SATP_DEFAULT_AA.ThedefaultPSPisVMW_PSP_FIXED.
WhenthesystemsearchestheSATPrulestolocateaSATPforagivendevice,itsearchesthedriverrules
first.Ifthereisnomatch,thevendor/modelrulesaresearched,andfinallythetransportrulesare
searched.Ifnomatchoccurs,NMPselectsadefaultSATPforthedevice.
IfVMW_SATP_ALUAisassignedtoaspecificstoragedevice,butthedeviceisnotALUAaware,noclaim
rulematchoccursforthisdevice.ThedeviceisclaimedbythedefaultSATPbasedonthedeviceʹs
transporttype.
ThedefaultPSPforalldevicesclaimedbyVMW_SATP_ALUAisVMW_PSP_MRU.TheVMW_PSP_MRUselectsan
active/optimizedpathasreportedbytheVMW_SATP_ALUA,oranactive/unoptimizedpathifthereis
noactive/optimizedpath.Thispathisuseduntilabetterpathisavailable(MRU).Forexample,ifthe
VMW_PSP_MRUiscurrently
usinganactive/unoptimizedpathandanactive/optimizedpathbecomes
available,theVMW_PSP_MRUwillswitchthecurrentpathtotheactive/optimizedone.
Table 4-1. Supported Path Policies
Policy Description
VMW_PSP_FIXED Thehostusesthedesignatedpreferredpath,ifithasbeenconfigured.Otherwise,thehost
selectsthefirstworkingpathdiscoveredatsystemboottime.Ifyouwantthehosttousea
particularpreferredpath,specifyitthroughthevSphereWebClient,orbyusingesxcli
storage nmp psp fixed deviceconfig set.See“Changing
PathPolicies”onpage 49.
ThedefaultpolicyforactiveactivestoragedevicesisVMW_PSP_FIXED.
Note:IfthehostusesadefaultpreferredpathandthepathʹsstatusturnstoDead,anewpath
isselectedaspreferred.However,ifyouexplicitlydesignatethepreferredpath,itwillremain
preferred
evenwhenitbecomesinaccessible.
VMW_PSP_MRU Thehostselectsthepaththatitusedmostrecently.Whenthepathbecomesunavailable,the
hostselectsanalternativepath.Thehostdoesnotrevertbacktotheoriginalpathwhenthat
pathbecomesavailableagain.ThereisnopreferredpathsettingwiththeMRU
policy.MRU
isthedefaultpolicyforactivepassivestoragedevices.
TheVMW_PSP_MRUrankingcapabilityallowsyoutoassignrankstoindividu alpaths.Toset
rankstoindividualpaths,usetheesxclistoragenmppspgenericpathconfigsetcommand.
Fordetails,seetheVMwareknowledgebasearticle2003468.
VMW_PSP_RR Thehost
usesanautomaticpathselectionalgorithmthatrotatesthroughallactivepaths
whenconnectingtoactivepassivearrays,orthroughallavailablepathswhenconnectingto
activeactivearrays.Automaticpathselectionimplementsloadbalancingacrossthephysical
pathsavailabletoyourhost.LoadbalancingistheprocessofspreadingI/O
requestsacross
thepaths.ThegoalistooptimizethroughputperformancesuchasI/Opersecond,megabytes
persecond,orresponsetimes.
VMW_PSP_RRisthedefaultforanumberofarraysandcanbeusedwithbothactiveactiveand
activepassivearraystoimplementloadbalancingacrosspathsfor
differentLUNs.
Table 4-2. Path Policy Effects
Policy Active/Active Array Active/Passive Array
MostRecentlyUsed Administratoractionisrequiredtofail
backafterpathfailure.
Administratoractionisrequiredtofailback
afterpathfailure.
Fixed VMkernelresumesusingthepreferred
pathwhenconnectivityisrestored.
VMkernelattemptstoresumebyusingthe
preferredpath.Thisactioncancausepath
thrashingorfailurewhenanotherSP
now
ownstheLUN.
RoundRobin Nofailback. Nextpathinroundrobinschedulingis
selected.