Establishing Sessions to a SAN

Dell PowerVault MD32xxi Configuration Guide for VMware ESX4.1 Server Software

3.More than one Network Interface Card (NIC) set aside for iSCSI traffic

4.No Distributed Virtual Switch (DVS) for iSCSI traffic

Not every environment requires all of the steps detailed in this whitepaper.

Users wishing to only enable Jumbo Frame support for the iSCSI connection need to follow steps 1 and steps 2 with the following changes:

Step 1: Configure vSwitch and Enable Jumbo Frames – No changes to the instructions

Step 2: Add iSCSI VMkernel Ports – Instead of assigning multiple VMkernel Ports, administrators will only assign a single VMkernel Port

Once these two steps are done, the rest of the configuration can be accomplished in the vCenter GUI by attaching NICs, assigning storage and then connecting to the storage.

The rest of this document assumes the environment will be using multiple NICs and attaching to a Dell PowerVault SAN utilizing Native Multipathing (NMP) from VMware.

Before continuing the examples, we first must discuss how VMware ESX4.1 establishes its connection to the SAN utilizing the new vSphere4 iSCSI Software Adapter. VMware uses VMkernel ports as the session initiators and so we must configure each port that we want to use as a path to the storage. This is independent of the number of network interfaces but in most configurations it will be a one-to-one relationship. 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.

Each volume on the PowerVault array can be utilized by ESX4.1 as either a Datastore or a Raw Device Map (RDM). To do this, the iSCSI software adapter utilizes the VMkernel ports that were created and establishes a session to the SAN and to the volume in order to communicate. With previous versions of ESX, this session was 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 this whitepaper.

Each VMkernel is bound to a physical adapter. Depending on the environment this can create a single session to a volume or up to 8 sessions (ESX4.1 maximum number of connections per volume). For a normal deployment, it is acceptable to use a one-to-one (1:1) ratio of VMkernels to physical network cards. This means if there are 3 physical NICs, you would establish 1 VMkernel per physical NIC and associate a separate NIC with each VMkernel port. In this example you would establish 3 sessions to a single volume on the SAN. 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 a volume but still utilizes the same physical NICs as the means to get to the volume. As more PowerVault members are added intelligent routing will come into the picture and allow for dynamic allocation of sessions as the SAN group grows.

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