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8 Configuring iSCSI Connectivity with VMware vSphere 6 and Dell PS Series Storage | TR1075
4 Establishing sessions to the SAN
Before continuing, we first must discuss how VMware ESXi establishes its connection to the SAN utilizing
the vSphere iSCSI software adapter. VMware uses VMkernel ports as the session initiators, so we must
configure each port that we want to use as a path to the storage. This configuration will be a one-to-one
(1:1) VMkernel-port-to-NIC relationship. Each session to the SAN will come from one VMkernel port which
will go out a single physical NIC. Once these sessions to the SAN are initiated, both the VMware NMP and
the Dell PS Series network load balancer will take care of load balancing and spreading the I/O across all
available paths.
Each volume on the PS Series array can be utilized by ESXi as either a datastore or a raw device mapping
(RDM). To do this, the iSCSI software adapter utilizes the VMkernel ports that were created and establishes
a session to the SAN and to that volume to communicate. Administrators have the ability to use additional
NICs for failover, but this document focuses on enabling NMP with Round Robin or preparation for third-
party multipathing with the Dell PS Series Multipathing Extension Module (MEM). With the improvements
to vSphere and MPIO, administrators can take advantage of multiple paths to the SAN for greater
bandwidth and performance. This does require some additional configuration which is discussed in detail
in this document.
Each VMkernel port is bound to a physical adapter. Depending on the environment, this can create a single
session to a volume or up to eight sessions (ESXi maximum number of paths to a volume). Use a one-to-
one (1:1) ratio of VMkernel ports to physical network cards. This means if there are two physical NICs, you
would establish one VMkernel per physical NIC, associating a separate NIC with each VMkernel port.
Looking at the following example, this means you would establish two sessions to a single volume on the
SAN. This trend can be expanded depending on the number of NICs in the system.
Note: vSphere MPIO iSCSI traffic cannot be routed. If your environment requires the routing of iSCSI
traffic then you must utilize Fixed path.
Figure 1 Example of iSCSI sessions using 1:1 VMkernel mapping with two physical NICs for iSCSI traffic
on a standard vSwitch