iSCSI allows three different ways to address both initiator and targets:

• iSCSI Qualified Name (IQN)
  • Format: iqn.yyyy-mm.{reversed domain name}
    • The most common format
    • Qualified by Date (yyyy-mm) due to domain name expiration or acquisition.
  • Example: iqn.2009-10.com.company:storage.winchester.sys1.xyz
  • Note: After the colon (":") is optional text for better descriptions.
  • Note: Provides naming compatibility with Fibre Channel and Serial Attached SCSI (SAS) [RFC 3980]
• Extended Unique Identifier (EUI)
  • Format: eui.{EUI-64 bit address}
  • Example: eui.35216B433947129A
  • Note: EUI are provided by the IEEE based on the EUI-64 Standard
• T11 Network Address Authority (NAA)
  • Format: naa.{NAA 64 or 128 bit identifier}
  • Example: naa.35216B433947129A
  • Note: Provided by the IEEE and is part OUI

An iSCSI participant is usually defined by three or four fields:

• IP Address (or Hostname) - Example: iscsi.company.net
• Port Number - Example: 3260
• iSCSI name - Example: iqn.2009-10.com.company:storage.winchester.sys1.xyz
• Optional CHAP Secret: - Example: ThisIsRealSafe

This is Hardware based initiator,  that is commonly combined with  Gigabit+ Ethernet NIC, a TCP/IP Offload Engine (TOE) and a SCSI bus adapter.

It is common for a iSCSI HBA to include the ability to boot to the devices oer the network.

The Initiator is also known as a Client, and acts in the same manner that a traditional SCSI bus, but without the physical limitations imposed by cabling.

The Initiator can be implemented in either Hardware or Software.

Hardware Initiator - Dedicated hardware used in conjuction with software, and sometimes firmware, to reduce the overhead associated with prcessing TCP and Ethernet interrupts, and generally increases performace.

Software Initiator - Generally this is a kernel level devices driver that works with the Operating Systems network stack and network card (NIC) to emulate SCSI commands, and is the common impletementation.

Is the abbreviation of Internet Small Computer System Interface, which uses standard SCSI commands to transfer data over the Internet Protocal (IP) to LANs, WANs and the Internet, and is not subject to the traditional cable limitations imposed by SCSI, and can be used on an existing network.

The most common ports use for iSCSI are TCP 860 and TCP 3260, and allow two hosts to exchange SCSI commands to create a Storage Area Network (SAN).

Because of the amount of data being transfered, there maybe a large performance reduction unless the SAN is setup on it's own dedicated network or subnet.

Typically, iSCSI is used for Storage Consolidation to a central location (Data Centers), or in a Disaster Recovery situation where one Data Center might be mirrowed to a remote location.

A LUN is an addressable portion of a larger SCSI device.

iSCSI initiators recognize a LUN as a raw SCSI or IDE hard drive.

In larger enterprise environments, these LUNs are usually setup on a large RAID array, called "slices", and are generally allocated to one client.

iSCSI does not restriction or have rules for multiple computers sharing one of these "slices". The filesystem and OS are responcible for the sharing of LUNs.

The iSCSI Target is the storage resource on the iSCSI server and is generally an array of hard drives.

TOE Cards are used as an alternative to a iSCSI HBA.

The TCP/IP operations are processed on the NIC insterad of the main computer CPU.

The processing of the iSCSI layer is still performed by the Host processor, but the CPU overhead is keep to a minimum.

• NetworkComputing.com - Storage Pipeline: How to Build an iSCSI Disk Array
• wikipedia.org - iSCSI