iSCSI is a network storage technology that enables the transmission of SCSI (Small Computer System Interface) commands over IP networks. It allows servers (initiators) to connect to remote storage devices (targets) via standard networking protocols, creating the illusion of a locally attached disk. This makes iSCSI an affordable, flexible, and scalable way to organize block-level storage in both local and distributed infrastructures.
iSCSI is considered an alternative to more expensive Fibre Channel-based solutions and is widely used in both enterprise and cloud environments. It is particularly relevant for building SANs (Storage Area Networks) without the need for specialized hardware.
How iSCSI works
iSCSI follows a client–server architecture:
- Initiator – a software or hardware component on the server side that initiates the connection and sends SCSI commands.
- Target – a storage device (e.g., NAS, RAID controller, or software-defined target) that receives the commands and returns the data.
Communication takes place over TCP/IP networks, making it possible to use standard Ethernet infrastructure without investing in Fibre Channel hardware.
Use cases for iSCSI
- Server and desktop virtualization (e.g., VMware vSphere, Microsoft Hyper-V)
- Backup and archival storage systems
- SAN environments for enterprise servers and databases
- Cloud platforms and data centers that require storage isolation and scalability
Advantages of iSCSI
- Utilizes standard networks: Runs over Ethernet and doesn’t require specialized infrastructure.
- Block-level access: Provides low-level, high-performance access to data, as opposed to file-level protocols like NFS or SMB.
- Scalability: New devices and capacity can be added easily.
- Flexibility: Supported by most operating systems, hypervisors, and virtualization platforms.
- Cost-effective: Eliminates the need for expensive Fibre Channel switches and HBA adapters.
In summary, iSCSI is a cost-effective and flexible solution for delivering block storage over IP networks. It is widely adopted in virtualized, cloud-based, and traditional IT infrastructures.