Round Robin path selection policy does not load all available paths as working paths.

Products

• VMware vSphere ESXi

Issue/Introduction

In this example, there are 4 paths available for the LUN, however only 2 show up as working. 

Available Paths:
esxcfg-mpath -b -d naa.6d039ea000b79f88000001cb66abb4d9
naa.6d039ea000b79f88000001cb66abb4d9 : LENOVO iSCSI Disk (naa.6d039ea000b79f88000001cb66abb4d9)
   vmhba64:C3:T0:L1 LUN:1 state:active iscsi Adapter: iqn.1998-01.com.vmware:localhost:1793773642:64  Target: IQN=iqn.2002-09.com.lenovo:thinksystem.6d039ea000b79f88000000006635daa9 Alias= Session=00023d00000b PortalTag=2
   vmhba64:C2:T0:L1 LUN:1 state:active iscsi Adapter: iqn.1998-01.com.vmware:localhost:1793773642:64  Target: IQN=iqn.2002-09.com.lenovo:thinksystem.6d039ea000b79f88000000006635daa9 Alias= Session=00023d000008 PortalTag=1
   vmhba64:C1:T0:L1 LUN:1 state:active iscsi Adapter: iqn.1998-01.com.vmware:localhost:1793773642:64  Target: IQN=iqn.2002-09.com.lenovo:thinksystem.6d039ea000b79f88000000006635daa9 Alias= Session=00023d000004 PortalTag=2
   vmhba64:C0:T0:L1 LUN:1 state:active iscsi Adapter: iqn.1998-01.com.vmware:localhost:1793773642:64  Target: IQN=iqn.2002-09.com.lenovo:thinksystem.6d039ea000b79f88000000006635daa9 Alias= Session=00023d000002 PortalTag=1

Working Paths:
root@esxi07:~] esxcli storage nmp device list
naa.6d039ea000b79f88000001cb66abb4d9
   Device Display Name: LENOVO iSCSI Disk (naa.6d039ea000b79f88000001cb66abb4d9)
   Storage Array Type: VMW_SATP_ALUA
   Storage Array Type Device Config: {implicit_support=on; explicit_support=off; explicit_allow=on; alua_followover=on; action_OnRetryErrors=off; {TPG_id=1,TPG_state=AO}{TPG_id=0,TPG_state=ANO}}
   Path Selection Policy: VMW_PSP_RR
   Path Selection Policy Device Config: {policy=rr,iops=1000,bytes=10485760,useANO=0; lastPathIndex=3: NumIOsPending=0,numBytesPending=0}
   Path Selection Policy Device Custom Config:
   Working Paths: vmhba64:C1:T0:L1, vmhba64:C3:T0:L1
   Is USB: false

 

You have followed article Considerations for using software iSCSI port binding in ESXi to confirm proper settings for iSCSI setup at the host level.
Re-scanning storage for the host or rebooting it does not change working path list.

Environment

vSphere ESXi 7.x
vSphere ESXi 8.x

Resolution

This is expected when the storage array is set on Active-Passive storage controller setup.

Additional Information

In this case, controller A was set to active and controller B was set to passive for device naa.6d039ea000b79f88000001cb66abb4d9 on storage array.
Chanel1 and channel3 are active-optimized paths, channel0 and channel2 are active-unoptimized paths. 
When controller A is down the array is capable of routing the traffic for this device through controller B but with comparatively less performance.