Best practices for connecting iSCSI initiators to a CLARiiON array



CLARiiON AX Series, CLARiiON CX Series,CLARiiON iSCSI Array, VNX, VNXe




When multiple NICs are used in a server, each NIC must be on a separate subnet: the same applies to iSCSI HBAs.VMware does not support more than one initiator or HBA for that host on each subnet and the Microsoft iSCSI Software Initiator default configuration ignores additional cards on the same subnet. PowerPath comes in two versions - Licensed and Unlicensed. With Licensed PowerPath, you can use more than one NIC/HBA on the host and two paths per NIC. With Unlicensed PowerPath you can ONLY use ONE NIC and two paths - one path to SPA and one path to SPB. Unlicensed PowerPath does not support load balancing.


If default connection is used, iSCSI will not load balance correctly when NIC cards are on the same subnet.




The following points are best practice for connecting iSCSI hosts to a CLARiiON or VNX

  • For iSCSI, there is no zoning (unlike an FC SAN) so separate subnets are used to provide redundant paths to the iSCSI ports on the CLARiiON array. For iSCSI you should have mini-SANs (VLANs) with only one HBA per host in each VLAN with one port per storage processor (SP) (for example, A0 and  B0 in one VLAN, A1 and  B1 in another).  All connections from a single server to a single storage system must use the same interface type, either NIC or HBA, but not both. 
  • It is good practice to create a separate, isolated IP network/VLAN for the iSCSI subnet. This is because the iSCSI data is unencrypted and also having an iSCSI-only network makes troubleshooting easier. 
  • If the host has only a single NIC/HBA, then it should connect to only one port per SP.  If there are more NICs or HBAs in the host, then each NIC/HBA can connect to one port from SP A and one port from SP B.  Connecting more SP ports to a single NIC can lead to discarded frames due to the NIC being overloaded.  
  • In the iSCSI initiator, set a different "Source IP" value for each iSCSI connection to an SP.  In other words, make sure that each NIC IP address only appears twice in the host's list of iSCSI Source IP addresses: once for a port on SP A and once for a port on SP B. 
  • Make sure that the Storage Process Management ports do not use the same subnets as the iSCSI ports - see emc235739 for more information. 
  • It is also best practice to use a different IP switch for the second iSCSI port on each SP.  This is to prevent the IP switch being a single point of failure.  In this way, were one IP switch to completely fail, the host can failover (via PowerPath) to the paths on the other IP switch.  In the same way, it would be advisable to use different switches for multiple IP connections in the host.  
  • Gateways can be used, but the ideal configuration is for HBA to be on the same subnet as one SP A port and one SP B port, without using the gateway.



Please refer to Primus article "emc156408" for more information on connecting iSCSI hosts to a CLARiiON or VNX.