iSCSI Storage Overview

With iSCSI, SCSI storage commands that your virtual machine issues to its virtual disk are converted into TCP/IP protocol packets and transmitted to a remote device, or target, on which the virtual disk is located. To the virtual machine, the device appears as a locally attached SCSI drive.

To access remote targets, the ESXi host uses iSCSI initiators. Initiators transport SCSI requests and responses between ESXi and the target storage device on the IP network. ESXi supports these types of initiators:

■	Software iSCSI adapter. VMware code built into the VMkernel. Allows an ESXi host to connect to the iSCSI storage device through standard network adapters. The software initiator handles iSCSI processing while communicating with the network adapter.

■	Hardware iSCSI adapter. Offloads all iSCSI and network processing from your host. Hardware iSCSI adapters are broken into two types.

■	Dependent hardware iSCSI adapter. Leverages the VMware iSCSI management and configuration interfaces.

■	Independent hardware iSCSI adapter. Leverages its own iSCSI management and configuration interfaces.

See the vSphere Storage documentation for details on setup and failover scenarios.

You must configure iSCSI initiators for the host to access and display iSCSI storage devices.

iSCSI Storage depicts hosts that use different types of iSCSI initiators.

■	The host on the left uses an independent hardware iSCSI adapter to connect to the iSCSI storage system.

■	The host on the right uses software iSCSI.

Dependent hardware iSCSI can be implemented in different ways and is not shown. iSCSI storage devices from the storage system become available to the host. You can access the storage devices and create VMFS datastores for your storage needs.

iSCSI Storage

Discovery Sessions

A discovery session is part of the iSCSI protocol. The discovery session returns the set of targets that you can access on an iSCSI storage system. ESXi systems support dynamic and static discovery.

■

Dynamic discovery. Also known as Send Targets discovery. Each time the ESXi host contacts a specified iSCSI storage server, it sends a Send Targets request to the server. In response, the iSCSI storage server supplies a list of available targets to the ESXi host. Monitor and manage with esxcli iscsi adapter discovery sendtarget or vicfg-iscsi commands.

■

Static discovery. The ESXi host does not have to perform discovery. Instead, the ESXi host uses the IP addresses or domain names and iSCSI target names (IQN or EUI format names) to communicate with the iSCSI target. Monitor and manage with esxcli iscsi adapter discovery statictarget or vicfg-iscsi commands.

For either case, you set up target discovery addresses so that the initiator can determine which storage resource on the network is available for access. You can do this setup with dynamic discovery or static discovery. With dynamic discovery, all targets associated with an IP address or host name and the iSCSI name are discovered. With static discovery, you must specify the IP address or host name and the iSCSI name of the target you want to access. The iSCSI HBA must be in the same VLAN as both ports of the iSCSI array.

Discovery Target Names

The target name is either an IQN name or an EUI name.

■	The IQN name uses the following format:

iqn.yyyy-mm.{reversed domain name}:id_string

For example: iqn.2007-05.com.mydomain:storage.tape.sys3.abc

The ESXi host generates an IQN name for software iSCSI and dependent hardware iSCSI adapters. You can change that default IQN name.

■	The EUI name is described in IETF rfc3720 as follows:

The IEEE Registration Authority provides a service for assigning globally unique identifiers [EUI]. The EUI-64 format is used to build a global identifier in other network protocols. For example, Fibre Channel defines a method of encoding it into a WorldWideName.

The format is eui. followed by an EUI-64 identifier (16 ASCII-encoded hexadecimal digits).

For example:

Type EUI-64 identifier (ASCII-encoded hexadecimal)

+- -++--------------+

| || |

eui.02004567A425678D

The IEEE EUI-64 iSCSI name format can be used when a manufacturer is registered with the IEEE Registration Authority and uses EUI-64 formatted worldwide unique names for its products.

Check in the UI of the storage array whether an array uses an IQN name or an EUI name.