iSCSI: Accessing Block Storage over IP Networks

Learn about iSCSI technology and how it enables access to block-level storage over standard IP networks. This guide explains the client-server model, benefits, and common use cases of iSCSI for building cost-effective and flexible storage area networks (SANs).

iSCSI: Accessing Storage Over IP Networks

What is iSCSI?

iSCSI (Internet Small Computer System Interface) is a networking technology that lets computers access block-level storage (like hard drives) over a standard Ethernet network using TCP/IP. This means you can connect to storage devices as if they were directly attached, even if they are located remotely. It's often called "SAN over IP" because it allows you to build a Storage Area Network (SAN) using your existing IP network infrastructure, reducing the need for specialized hardware and simplifying deployment.

How iSCSI Works

iSCSI uses a client-server model:

  1. Initiator Request: A computer (the iSCSI initiator) sends a request to access storage to the storage device (the iSCSI target).
  2. SCSI-to-iSCSI Translation: The target translates standard SCSI commands (the language for communicating with storage) into iSCSI commands.
  3. Data Transmission: Data is transmitted over the IP network as iSCSI Protocol Data Units (PDUs).
  4. iSCSI-to-SCSI Translation: The receiving side translates the iSCSI commands back into SCSI commands and then gives the appropriate commands to the storage device.
  5. Data Retrieval: The data is retrieved from the storage device.

Advantages of iSCSI

  • Cost-Effective: Uses standard TCP/IP networking, eliminating the need for specialized hardware (like Fibre Channel HBA cards).
  • Flexible: Allows for long-distance storage access.
  • Standard Ethernet Compatibility: Leverages existing network infrastructure.
  • Reusability of Existing Hardware: Existing servers can be used as iSCSI targets.
  • High Performance: Block-level access is often faster than file-level protocols (like NFS).
  • Simple Configuration: Relatively easy to set up and manage.

Conclusion

iSCSI is a powerful technology that provides a flexible and cost-effective way to access storage over IP networks. Its simplicity, speed, and ability to leverage existing network infrastructure have made it a widely adopted solution for both small and large organizations.