This article will give you a brief overview of iSCSI – Internet Small Computer Systems Interface protocol, the way the protocol works and the most important components of the iSCSI protocol.
What is iSCSI – Internet Small Computer Systems Interface?
iSCSI is a Transport Layer protocol that works over the TCP/IP (Transmission Control Protocol/Internet Protocol) suite.
Storage devices such as Hard Disks and USB drives connect directly to the desktops and laptops but not under iSCSI technology. The iSCSI technology separates the Storage devices from the Host Systems that access those storage devices.
iSCSI Protocol facilitates data access requests from the Host Systems (iSCSI Initiator) to the Storage Devices (iSCSI Targets) and back. The iSCSI hosts (iSCSI Initiator) uses iSCSI commands to access the data residing on remote iSCSI storage devices (iSCSI Target).
iSCSI is a Storage Area Networking (SAN) protocol and defines how the data flows between host systems and storage devices which don’t have direct connection to the host system.
The iSCSI protocol basically carries SCSI commands over Standard Ethernet IP networks.
iSCSI supports Block-Level storage, i.e. the iSCSI storage devices store the data at Block-Level.
In essence, iSCSI allows two hosts to negotiate and then exchange SCSI commands using Internet Protocol (IP) networks.
Some SAN protocols require special cabling or connectivity devices but iSCSI doesn’t.
Since iSCSI runs on top of TCP/IP protocol, it can run smoothly using the existing IP Infrastructure in an organization.
We can use iSCSI to transmit data over Local Area Network (LANs), Wide Area Networks (WANs). We can also enable location independent storage and retrieval of data by using iSCSI.
How iSCSI – Internet Small Computer Systems Interface works?
iSCSI – Sender’s Side
The application initiates an iSCSI request which goes to the Operating System. The Operating System generates an appropriate iSCSI command and data request.
The operating system then encapsulates the command and data request and encrypted, if needed.
The Session Layer adds a Packet Header to the encapsulated and encrypted (if applicable) data.
Once the Packet Header is added by the Session Layer, the resulting IP packets are transmitted over an ethernet connection.
iSCSI – Receiver’s Side
On the receivers side, the iSCSI receiver decrypts, the IP Packet which it receives, if encrypted by the sender.
Once the receiver decrypts the IP Packet, it disassembles the IP Packet and separates SCSI commands and Data request.
The SCSI commands are sent to the SCSI controller, and the SCSI controller sends the commands to the storage device.
Port Number used by iSCSI:
By default, iSCSI uses TCP port 3260
What are the Components of iSCSI – Internet Small Computer Systems Interface?
IP Network
iSCSI Initiator
An iSCSI Initiator is a component present on the iSCSI client side that provides connectivity to the remote iSCSI Target.
The iSCSI Initiator software is already present in Windows Operating System.
iSCSI Target
iSCSI Qualified Name (IQN)
Follow the link mentioned below for more information about iSCSI from Microsoft: https://learn.microsoft.com/en-us/training/modules/implement-windows-server-iscsi/2-list-functionalities-components-use-cases