Internet Small Computer System Interface (iSCSI)

What is iSCSI (Internet Small Computer System Interface)?

The Internet Small Computer System Interface, or iSCSI in short, refers to the Internet Protocol (IP) for transferring data through different types of networks such as LAN, WAN, and SAN by using storage arrays in the data centers.

Technically, iSCSI is a Transmission Control Protocol/Internet Protocol (TCP/IP) or a data transport layer protocol that defines exactly how the Small Computer System Interface (SCSI) packets should be transmitted over the protocol.

Understanding iSCSI (Internet Small Computer System Interface)

What is iSCSI

Internet Small Computer System Interface is the Internet Protocol for data transfer for the internet itself and different other networks, such as:

Ideally, this is mainly due to the enhanced performance offered by the SANs in terms of data retrieval, in particular.

However, iSCSI does not support accessing Network Attached Storage (NAS) or object storage due to their varied transfer protocols.

Still, in terms of block storage performance, the Internet Small Computer System Interface protocol offers reasonably good performance at a low cost.

Typically, most of the storage based on this particular interface data transfer protocol is hard disk storage. However, there are quite a few tape-based and medium changer devices available on the market as well.

Usually, in iSCSI, the most commonly used transport is TCP/IP over Ethernet, but it also allows using Remote Direct Memory Access (RDMA) with iSER, which is actually the short form of the iSCSI Extension for RDMA.

However, while using it with iSER, the transport is either InfiniBand or RDMA over Converged Ethernet (RoCE), where the underlying network for each is InfiniBand and Ethernet, respectively.

Typically, iSCSI can be expedited through the network adapters that come with an iSCSI hardware offload and, optionally, with a TCP Offload Engine (TOE).

The HBA in the former offloads the functions of the iSCSI initiator to the Central Processing Unit (CPU) of the server.

And in the latter case, TCP processing is offloaded by the adapter from the CPU and the server kernel.

Operating System Support

It is supported by different major operating systems and hypervisors, such as:

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While working, this is what happens at the receiving end of the iSCSI system:

On the other hand, at the receiving side of the data packet, this is what happens:

Since iSCSI is a bi-directional protocol, it can be used to send data in return for a response to an initial request as well.


There are basically two major components of iSCSI. These are:


Ideally, for iSCSI performance, the base configuration considered is 10 GbE, though most of its applications are built on a 1 Gigabit per second Ethernet (GbE) structure.

The multipathing technique allows setting up various paths between the storage resources and the client servers by a storage administrator for the following benefits:

Other techniques that enhance the performance of iSCSI are:


Here are some Ethernet alternatives to iSCSI:

What is iSCSI Used for?

The Internet Small Computer System Interface protocol is mainly used to create a shared storage network used by multiple clients and servers to allow them access to a central storage resource.

Ideally, the first storage based on iSCSI was used in 2000 with Windows NT. It was followed by IBM with a Linux operating system in 2001. After that, it has been available for other operating systems.

It is the features of iSCSI that make it so popular as a Tier-2 application for shared storage among different hosts that need good, if not the best, block storage performance.

Allowing the users to consolidate their data through different storage arrays of the data centers, this particular protocol makes it look like they are using a local hard disk for storage and not that of a data center storage.

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You can also use it with almost all types of enterprise storage arrays.

The protocol is also usable with special types of Host Bus Adapters (HBAs) and even with regular Network Internet Cards (NICs).

It is extensively used among the large cloud service providers and the hyperscalers with the help of a block storage solution over Ethernet.

Ideally, iSCSI is best to use when:

Can iSCSI be Encrypted?

Yes, the data transferred through iSCSI can be encrypted to ensure the confidentiality of information sent over this framework.

Ideally, data integrity in iSCSI is provided at five different levels, such as:

How To Connect to iSCSI Storage?

Ideally, to use the Internet Small Computer Systems Interface storage, you will have to connect the iSCSI target to the Windows iSCSI initiator.

This will show the volume on the computer system as a local physical hard drive. You can use this for video storage as well.

The steps to follow to go ahead are:

When the changes are successful, the status will change to Connected.



iSCSI Vs Fiber Channel

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Questions & Answers:


The Internet Small Computer System Interface is typically a Transmission Control Protocol (TCP) and not a User Datagram Protocol (UDP).

Is iSCSI a Block or File?

The Internet Small Computer System Interface is a block protocol rather than a file protocol. For every volume, this protocol supports one single client on the server, but it allows the applications to run on the machine of the single client while sharing remote data.

What Port Does iSCSI Use?

The iSCSI protocol typically uses TCP 3260 ports for the protocol itself, along with names of higher levels for addressing the objects in it.

Since the protocol is constructed in Clustered Data ONTAP (Open Network Technology for Appliance Products), it does not allow altering the port number.

Typically, the port number 3260 is registered as a specific part of its specification. Usually, this port cannot be used by any other service or application.

What are the Types of iSCSI?

There are basically three types of Internet Small Computer System Interface protocol, and special name formats are used to identify its targets as well as the initiators.

The types include the Extended Unique Identifier (EUI), iSCSI Qualified Name (IQN), and T11 Network Address Authority (NASA). However, for all three types the switches are very similar to those of the Ethernet network TCP/IP.

Is iSCSI IP Based?

Yes, iSCSI is IP-based and is standardized by the Internet Engineering Task Force and is described by RFC 3720.

This IP-based standard transfers data that supports host access. It allows carrying Small Computer System Interface commands via different IP networks.

What OSI layer is iSCSI?

Typically, the Internet Small Computer System Interface protocol functions on layer 5, or the Session layer of the International Organization of Standardization – Open System Interconnection (ISO-OSI) model.

Characteristically, the SCSI commands produced at the presentation layer make their way ultimately through the physical layer in order to communicate with other devices via iSCSI.

What is the Speed of iSCSI?

Typically, the Internet Small Computer System Interface protocol uses the traditional Ethernet switches and cables and therefore can operate at different speeds such as 1 GB/s, 10 GB/s, 40 GB/s, and sometimes more.

Do People Still Use iSCSI?

Yes, people still use the Internet Small Computer Systems Interface data transfer protocol because most of the infrastructures available today depend on the iSCSI standard to link the storage with the servers.

This is the network version of the bus SCSI protocol and helps to transmit the SCSI commands over the TCP/IP network to provide the users with block-level access to the shared and centralized storage devices.


iSCSI is a useful data transfer and storage protocol. It offers reliable, predictable, and improved performance.

Its popularity has grown because of the rising need for better traffic congestion management and Quality of Service (QoS) and the need for faster speeds on Ethernet switches.