StarWind is a hyperconverged (HCI) vendor with focus on Enterprise ROBO, SMB & Edge

What is iSCSI?

  • November 14, 2023
  • 15 min read
StarWind Solutions Engineer. Diana possesses comprehensive technical knowledge of various storage types and expertise in building and optimizing virtualized environments.
StarWind Solutions Engineer. Diana possesses comprehensive technical knowledge of various storage types and expertise in building and optimizing virtualized environments.

Internet Small Computer System Interface Protocol (iSCSI) – is a protocol that allows SCSI commands to be transmitted over TCP, enabling remote storage to be connected to servers as if they were local disks.  The iSCSI protocol essentially enables the creation of Storage Area Networks (SANs) on existing IP networks. What this does is eliminate the need for separate, dedicated storage networks. To this day, lots of experts view iSCSI as a less expensive alternative to Fibre Channel.

The iSCSI protocol essentially enables the creation of Storage Area Networks (SANs) on existing IP networks

iSCSI Components: Initiator and Target

An iSCSI setup has two main components – the iSCSI initiator and the ISCSI target that communicate with each other to enable data transfer:


The iSCSI initiator is a software or hardware component on the client’s machine within the storage network. Software ISCSI initiators can be used with standard Ethernet equipment to create the storage network and connect to multiple iSCSI targets via multiple paths in parallel.


The iSCSI target is a service that runs on the server and provides access to its storage resources. iSCSI targets allow to expose local storage as SCSI LUNs to connected iSCSI initiators. The iSCSI target server supports multiple parallel connections from multiple initiators, meaning that single storage server can provide storage to multiple connected clients.

How Does iSCSI Work

iSCSI encapsulates the SCSI commands and assembles block-level data in packets for the TCP/IP layer, which are then used to provide communication and data transfer between storage devices.  Block-level data is carried from the iSCSI initiator on the server to an iSCSI target on a storage device.  On the receiving side, the iSCSI protocol will then separate the SCSI commands, and the operating system will treat the storage as a locally connected device.

iSCSI Performance

The performance of an iSCSI system depends on lot of different factors, including the speed of the network, the configuration of the storage array, and the workload characteristics. In most cases, iSCSI offers excellent performance, especially when implemented over high-speed RDMA-enabled networks.

To get the most out of your setup, 10 GbE or faster equipment should be used as the base configuration, especially if you want to compete with the speeds of Fibre Channel storage networks.

Another way to improve the performance of iSCSI is through multipathing. Multipathing is a process that enables iSCSI storage traffic to run over multiple paths between the initiator and targets. This feature enhances performance and makes accessing the storage more efficient because total bandwidth can be distributed among multiple paths to balance the workload.

Jumbo frames is another important Ethernet protocol setting that permits iSCSI storage systems to transfer larger amounts of data per single Ethernet frame, which improves performance.

Benefits of Using iSCSI and iSCSI Storage

Implementing iSCSI storage solutions offers several benefits to companies, including:

Cost-Effectiveness: iSCSI uses standard Ethernet and does not need complex, expensive cards and switches. That is why it is considered a cheaper option than Fibre Channel networks.

Flexibility and Scalability: Admins can expand the storage to meet the needs of the business. This makes it a scalable option for companies of various sizes.

Simplified Management: Centralized storage systems facilitate easier management and maintenance, allowing for streamlined operations and reduced downtime.

iSCSI vs Fibre Channel

Fibre Channel and iSCSI are popular and effective in transferring large amounts of data. They are technologies created to solve the same technical problems of networking block storage. However, over time, they have become fierce competitors. Here are some of their differences and similarities:

Feature iSCSI Fibre Channel
Block-level storage Yes Yes
Allows for use on existing network Yes No
Strong data flow management (CRC check, avoids transmission retries) No Yes
Less expensive Yes No
Well suited for high input / output apps No Yes
Embedded service infrastructure No Yes
Labor-intensive and complex to deploy No Yes

iSCSI Storage vs. NAS Storage

ISCSI and NAS were designed to meet the need for ever-increasing demand for storage capacity using scalable, external storage devices. However, NAS is a way to add and connect storage in a shared network, while iSCSI is a data transport protocol.

Feature NAS iSCSI
Data access level Object-level Block-level
Overall performance Depends on the SMB version used or NFS. LAN infrastructure plays a key role. Supports 10 GbE-based SAN or even higher
Complexity of implementation Configuration is not complex and can be done effortlessly provided you carefully configure built-in server Not complex to implement. With Windows Server, for example, it comes with the existing list of roles and features
Directly accessible by clients Just enter the path of the shared folder. The iSCSI software needs to be first configured and mapped as a device


Ready for HA clusters Supported by just a few server cluster technologies that support SMB/NFS storage as a shared volume Support by almost all clustering technologies

How to Implement iSCSI Storage

Implementing iSCSI storage involves several steps:

  • Infrastructure Assessment- Evaluate the existing network infrastructure, ensuring it can adequately support an iSCSI storage system. This generally involves configuring switches and routers to allow iSCSI traffic. StarWind vSAN can significantly help simplify the process of setting up and managing iSCSI storage.
  • Selecting Suitable Hardware and Software – Choose appropriate storage devices and software that align with the company’s storage needs and objectives.
  • Configuration – Set up the iSCSI initiators and targets and configure the network settings to facilitate optimal performance. To improve performance while maintaining a low latency, StarWind iSCSI Accelerator/Load Balancer is a good option. It is designed to balance iSCSI among multiple CPU cores that works right after deployment in conjunction with Microsoft iSCSI Initiator and iSCSI SAN.
  • Testing – Conduct rigorous testing to ensure the setup meets the performance and reliability standards necessary for your operations.

What are iSCSI Limitations?

While iSCSI offers numerous benefits, it is not without limitations:

  1. Network Dependency: Because iSCSI is dependent on IP networks, the performance of this protocol can be affected by network congestion and outages.
  2. Security Concerns: If proper security protocols are not implemented, data transmitted over networks can be vulnerable to unauthorized access and cyber-attacks.
  3. Potential Complexity: Management can become challenging in complex setups, requiring specialized knowledge and skills. However, it is still less complicated than dealing with large enterprise SAN networks and the corresponding equipment.

Alternatives to iSCSI

Before settling on iSCSI, there are other storage solutions that you can check to know if they will suit your business needs:

  • Fibre Channel: As discussed, a high-speed network solution for SANs. If you already have a working FC SAN setup that does its job, you may want to skip on implementing iSCSI SAN. It’s always better to avoid having multiple heterogenous systems serving single purpose.
  • NAS: Ideal for centralized file sharing and small-scale deployments without performance-hungry applications.


Storage Area Network

SAN is a dedicated network that is used for block-level data storage. Unlike a typical local area network (LAN) that connects computers, a SAN connects servers to data storage devices. This allows multiple servers to access shared storage as if it were a direct-attached drive. SAN is typically used in data centers and enterprise environments where there’s a need for high-speed, block-level access to large volumes of data.

Network Attached Storage

NAS is a central storage location accessible to any device on your network you give access to. This way, multiple users and clients can access and share files within the same network from different devices.  To keep it simple – NAS is like SAN, but instead of block-level access, it operates on the file level.


Within the iSCSI system, the LUN (Logical Unit Number) is a unique identifier for an individual or a group of hard disk drives, facilitating data management and isolation within a larger storage array. It enables the connected client (iSCSI initiator) to differentiate and appropriately manage various storage devices on the storage server (iSCSI target).

Virtual Storage Target

A virtual storage target refers to the simulation of multiple storage devices managed as a single unit, thereby optimizing storage resources and facilitating data management through virtualization technologies.


Data transfer has always been vital since the advent of computers. However, the amount, speed, and method of the transfer is what has been changing over the years. Choosing the right storage system is crucial for the efficient operation of any business in this data-driven world. As we have seen above, iSCSI presents a cost-effective, scalable, and flexible storage solution, leveraging existing IP networks to facilitate data storage and management. Even though it may have limitations, with proper implementation and management, iSCSI can serve as a vital tool in your company’s data management arsenal, fostering growth and innovation in your business ventures.

This material has been prepared in collaboration with Asah Syxtus Mbuo, Technical Writer at StarWind.

Found Diana’s article helpful? Looking for reliable, high-performance software-defined HA iSCSI storage for your infrastructure?
Dmytro Malynka
Dmytro Malynka StarWind Virtual SAN Product Manager

We’ve got you covered! StarWind Virtual SAN (VSAN) is specifically designed to provide highly available iSCSI and NVMe-oF storage for Hyper-V, vSphere, and KVM clusters. With StarWind VSAN, simplicity is key: utilize the local disks of your hypervisor hosts and create shared HA storage for your VMs. Interested in learning more? Book a short StarWind VSAN demo now and see it in action!