Dell PowerVault MD3200i - Page 9

Dell PowerVault MD3200i/MD3600i Configuration Guide for VMware ESX4.1 Server Software
June 4, 2012 Page 9
ESTABLISHING SESSIONS TO A SAN
Before continuing the examples, we first must discuss how VMware ESX4.1 establishes
its connection to the SAN utilizing the vSphere4 iSCSI Software Adapter.
With previous versions of ESX, sessions were established using a single NIC path and any
additional NICs were there for failover only. With the improvements to vSphere4 and
MPIO, administrators can now 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 the sections below.
VMware uses VMkernel ports as the session initiators. Each VMkernel is bound to a
separate physical adapter. Depending on the environment this can create a single
session to an array or up to eight sessions (ESX4.1 maximum number of connections per
volume). For a typical deployment, it is recommended to use a one-to-one (1:1) ratio of
VMkernels to physical network cards. As shown in Figure 2 below, this means if there
are four physical NICs, you would establish one VMkernel per physical NIC and associate
a separate NIC with each VMkernel port.
This scheme can be expanded depending on the number of NICs you have in the system.
As the environment grows, you can establish multiple sessions to the SAN by
oversubscribing VMkernel ports to actual physical NICs. This establishes multiple
sessions to an array but still utilizes the same physical NICs as the means to get to the
storage. However, VMWare reports issues
with oversubscribing VMkernel ports.
Consequently we recommend maintaining a 1:1 port binding.
Once these sessions to the SAN are initiated, the VMware NMP will take care of load
balancing and spreading the I/O across all available paths.
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
.