From the Dell white paper on MD_iSCSI_Deploymnet:
Considerations involving subnet configurationIt is recommended that you have different ports on different subnets due to throughput and pathing considerations. The decision to use multiple subnets may depend upon the specific architecture and networking topology and may not be essential in all cases. On the MD3200i/MD3600i, setup each port on a different subnet with one disk group per controller, each disk group with one LUN per port.Multiple subnets should be allocated by the number of array ports per controller. With the MD3200i you only get an active path to multiple ports on the same controller if they are on different subnets or VLANs. Since the MD3220i has four ports per controller you get your best throughput with four subnets.On an MD3200i/MD3600i, the LUNs are assigned out of disk groups. Only one controller at a time has access to the LUNs. The alternate controller has access to those LUNs but only as a failover alternate path. This LUN/controller relationship is reported by the MD3200i/MD3600i to VMware which then dictates the paths (and the "optimal" condition of the array).Regardless of the pathing method in VMware, you will only have one active port on each controller of the array if you do not create additional subnets. Without additional subnets that will cause a bottle-neck at the controller since pathing is at the disk group level rather than the LUN level for the MD300xiConfiguring RR to the same LUN across both controllers is not recommended.
This will be why it was setup with four subnets per controller. At present we only have 2 pnics per ESXi host avaiable for iSCSI so with this in mind I'm going with the following:
vSwitch1:
vmk1 IP: 192.168.132.105 (Port Binding vmnic 1)
vSwitch2:
vmk2 IP: 192.168.133.105 (Port Binding vmnic 2)
Storage array:
Controller 0/1: 192.168.130.100
Controller 0/2: 192.168.131.100
Controller 0/3: 192.168.132.100 (Static Discovery from ESXi host)
Controller 0/4: 192.168.133.100 (Static Discovery from ESXi host)
Controller 1/1: 192.168.130.101
Controller 1/1: 192.168.131.101
Controller 1/1: 192.168.132.101 (Static Discovery from ESXi host)
Controller 1/1: 192.168.133.101 (Static Discovery from ESXi host)
This will allow two additional pnics in furture if needed. The only difference I can see from the whitepaper recommeded configuration and what was already in place is Dymanic Discovery (ESXi host aware of paths it can't reach) and a single vSwitch for vmk ports.
I'll be testing the above first as its recomended configuration in Dell whitepaper but I'm still perplexed at this note:
4. Note: Port binding requires that all target ports of the storage array must reside on the same broadcast domain as the VMkernel ports because routing is not supported with port binding. See VMware KB #2017084 here.
This is right under a graphic showing the following networking configuration using different subnets:
vSwitch1:
vmk1 IP: 172.20.2.11 vmnic1
vSwitch2:
vmk2 IP: 172.21.2.11 vmnic3
vSwitch3:
vmk2 IP: 172.22.2.11 vmnic5
vSwitch4:
vmk2 IP: 172.23.2.11 vmnic7