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ESX Configuration Guide

How Virtual Machines Access Storage

When a virtual machine communicates with its virtual disk stored on a datastore, it issues SCSI commands. Because datastores can exist on various types of physical storage, these commands are encapsulated into other forms, depending on the protocol that the ESX host uses to connect to a storage device.

ESX supports Fibre Channel (FC), Internet SCSI (iSCSI), Fibre Channel over Ethernet (FCoE), and NFS protocols. Regardless of the type of storage device your host uses, the virtual disk always appears to the virtual machine as a mounted SCSI device. The virtual disk hides a physical storage layer from the virtual machine’s operating system. This allows you to run operating systems that are not certified for specific storage equipment, such as SAN, inside the virtual machine.

Figure 7-3 depicts five virtual machines using different types of storage to illustrate the differences between each type.

Figure 7-3. Virtual machines accessing different types of storage

 

 

Host

 

 

 

 

requires TCP/IP connectivity

virtual

virtual

virtual

virtual

virtual

machine

machine

machine

machine

machine

 

local

 

 

 

 

ethernet

 

 

 

 

SCSI

 

software

 

 

 

 

 

 

fibre

iSCSI

adapter

 

 

 

 

VMFS

channel

ethernet

ethernet

HBA

HBA

 

 

NIC

NIC

 

SAN

LAN

LAN

LAN

Key

physical disk

datastore

 

 

 

virtual

VMFS

VMFS

NFS

fibre array

iSCSI array

NAS appliance

disk

 

 

 

NOTE This diagram is for conceptual purposes only. It is not a recommended configuration.

Comparing Types of Storage

Whether certain vSphere functionality is supported might depend on the storage technology that you use. Table 7-1 compares networked storage technologies that ESX supports.

Table 7-1. Networked Storage that ESX Supports

Technology

Protocols

Transfers

Interface

 

 

 

 

Fibre Channel

FC/SCSI

Block access of data/LUN

FC HBA

 

 

 

 

 

iSCSI

IP/SCSI

Block access of data/LUN

n

iSCSI HBA (hardware iSCSI)

 

 

 

n

NIC (software iSCSI)

 

 

 

 

NAS

IP/NFS

File (no direct LUN access)

NIC

 

 

 

 

 

Table 7-2 compares the vSphere features that different types of storage support.

86

VMware, Inc.

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