Chapter 7 Introduction to Storage

	To connect to the FC SAN, your host should be equipped with Fibre Channel
	host bus adapters (HBAs). Unless you use Fibre Channel direct connect storage,
	you need Fibre Channel switches to route storage traffic. If your host contains
	FCoE (Fibre Channel over Ethernet) HBAs, you can connect to your shared
	Fibre Channel devices using an IP network.
Internet SCSI (iSCSI)	Stores virtual machine files on remote iSCSI storage devices. iSCSI packages
	SCSI storage traffic into the TCP/IP protocol so that it can travel through
	standard TCP/IP networks instead of the specialized FC network. With an iSCSI
	connection, your host serves as the initiator that communicates with a target,
	located in remote iSCSI storage systems.
	ESX offers the following types of iSCSI connections:
	Hardware iSCSI	Your host connects to storage through a third-party
		adapter capable of offloading the iSCSI and network
		processing.
	Software iSCSI	Your host uses a software-based iSCSI initiator in the
		VMkernel to connect to storage. With this type of iSCSI
		connection, your host needs only a standard network
		adapter for network connectivity.
Network-attached	Stores virtual machine files on remote file servers accessed over a standard
Storage (NAS)	TCP/IP network. The NFS client built into ESX uses Network File System (NFS)
	protocol version 3 to communicate with the NAS/NFS servers. For network
	connectivity, the host requires a standard network adapter.
Shared Serial Attached	Stores virtual machines on direct-attached SAS storage systems that offer
SCSI (SAS)	shared access to multiple hosts. This type of access permits multiple hosts to
	access the same VMFS datastore on a LUN.

Supported Storage Adapters

Storage adapters provide connectivity for your ESX host to a specific storage unit or network.

Depending on the type of storage you use, you might need to install or enable a storage adapter on your host. ESX supports different classes of adapters, including SCSI, iSCSI, RAID, Fibre Channel, Fibre Channel over Ethernet (FCoE), and Ethernet. ESX accesses the adapters directly through device drivers in the VMkernel.

Target and Device Representations

In the ESX context, the term target identifies a single storage unit that the host can access. The terms device and LUN describe a logical volume that represents storage space on a target. Typically, the terms device and LUN, in the ESX context, mean a SCSI volume presented to the host from a storage target and available for formatting.

Different storage vendors present the storage systems to ESX hosts in different ways. Some vendors present a single target with multiple storage devices or LUNs on it, while others present multiple targets with one LUN each.

Figure 7-1. Target and LUN Representations

	target		target	target	target
LUN	LUN	LUN	LUN	LUN	LUN
	storage array			storage array

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ESX Configuration Guide

In this illustration, three LUNs are available in each configuration. In one case, the host sees one target, but that target has three LUNs that can be used. Each LUN represents an individual storage volume. In the other example, the host sees three different targets, each having one LUN.

Targets that are accessed through the network have unique names that are provided by the storage systems. The iSCSI targets use iSCSI names, while Fibre Channel targets use World Wide Names (WWNs).

NOTE ESX does not support accessing the same LUN through different transport protocols, such as iSCSI and Fibre Channel.

A device, or LUN, is identified by its UUID name. If a LUN is shared by multiple hosts, it must be presented to all host with the same UUID.

Understanding Fibre Channel Naming

In Fibre Channel SAN, a World Wide Name (WWN) uniquely identifies each element in the network, such as a Fibre Channel adapter or storage device.

The WWN is a 64-bit address that consists of 16 hexadecimal numbers and might look like this:

20:00:00:e0:8b:8b:38:77 21:00:00:e0:8b:8b:38:77

The WWN is assigned to every Fibre Channel SAN element by its manufacturer.

Understanding iSCSI Naming and Addressing

In an iSCSI network, each iSCSI element that uses the network has a unique and permanent iSCSI name and is assigned an address for access.

iSCSI Name

Identifies a particular iSCSI element, regardless of its physical location. The iSCSI name can use IQN or EUI format.

nIQN (iSCSI qualified name). Can be up to 255 characters long and has the following format: iqn.yyyy-mm.naming-authority:unique name

yyyy-mm	The year and month when the naming authority was established.
naming-authority	Usually reverse syntax of the Internet domain name of the naming
	authority. For example, the iscsi.vmware.com naming authority could have
	the iSCSI qualified name form of iqn.1998-01.com.vmware.iscsi. The name
	indicates that the vmware.com domain name was registered in January of
	1998, and iscsi is a subdomain, maintained by vmware.com.
unique name	Any name you want to use, for example, the name of your host. The naming
	authority must make sure that any names assigned following the colon are
	unique. For example, iqn.1998-01.com.vmware.iscsi:name1.

nEUI (extended unique identifier). Includes the eui. prefix, followed by the 16-character name. The name includes 24 bits for the company name assigned by the IEEE and 40 bits for a unique ID, such as a serial number.

For example, eui.0123456789ABCDEF

iSCSI Alias

A more manageable, easy-to-remember name to use instead of the iSCSI name. iSCSI aliases are not unique, and are intended to be just a friendly name to associate with the node.

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