‘What is iSCSI and How Does it Work?’

A Comprehensive Guide to this Storage Network Protocol

ISCSI, or Internet Small Computer System Interface, is a storage network protocol that enables the transfer of data between servers and storage systems over a standard IP network. ISCSI is an alternative to traditional Fibre Channel storage networks and offers several advantages, including cost savings, ease of implementation, and flexibility.

ISCSI Architecture

ISCSI architecture consists of three main components:

  1. Initiator: The initiator is the software or hardware component that sends ISCSI commands to the target. It can be installed on a server or a client machine.
  2. Target: The target is the storage system or disk array that responds to the initiator’s requests. It provides block-level access to the data stored on it.
  3. ISCSI HBA or Adapter: The ISCSI HBA or adapter is a hardware component that connects the initiator to the network. It converts ISCSI commands into Ethernet frames and vice versa.

ISCSI Protocol

ISCSI protocol uses TCP/IP for transport and SCSI (Small Computer System Interface) commands for data transfer. It establishes a connection between the initiator and the target using TCP and sends SCSI commands over this connection.

ISCSI Initiator Process

The ISCSI initiator process involves the following steps:

  1. Discovery: The initiator discovers the target using various methods like multicast discovery, static discovery, or DHCP discovery.
  2. Login: The initiator logs in to the target using CHAP (Challenge-Handshake Authentication Protocol) or other authentication methods.
  3. Session Establishment: The initiator establishes a session with the target using TCP.
  4. Command Exchange: The initiator sends SCSI commands to the target, and the target responds with data or status information.
  5. Session Termination: The initiator terminates the session when it is no longer needed.

ISCSI Target Process

The ISCSI target process involves the following steps:

  1. Discovery: The target listens for ISCSI discovery messages and responds to them.
  2. Login: The target authenticates the initiator using CHAP or other authentication methods.
  3. Session Establishment: The target establishes a session with the initiator using TCP.
  4. Command Processing: The target processes the SCSI commands received from the initiator and sends the data or status information back.
  5. Session Termination: The target terminates the session when it is no longer needed.

ISCSI Advantages

ISCSI offers several advantages over traditional Fibre Channel storage networks:

  1. Cost Savings: ISCSI uses standard Ethernet networks, which are less expensive than Fibre Channel networks.
  2. Ease of Implementation: ISCSI is easier to implement than Fibre Channel because it uses existing IP networks and does not require specialized hardware.
  3. Flexibility: ISCSI offers more flexibility than Fibre Channel because it can be used with various storage systems and servers.
  4. Scalability: ISCSI is more scalable than Fibre Channel because it can be easily extended by adding more switches and hosts to the network.

ISCSI Disadvantages

ISCSI also has some disadvantages:

  1. Lower Performance: ISCSI has lower performance than Fibre Channel because it uses TCP/IP for transport and adds additional overhead.
  2. Lack of Standardization: There is no standard ISCSI hardware interface, which can make it difficult to compare and choose products.
  3. Security Concerns: ISCSI uses TCP/IP for transport, which can make it vulnerable to network attacks.

Conclusion

ISCSI is a popular storage network protocol that offers several advantages over traditional Fibre Channel storage networks. It uses standard IP networks, is easier to implement, and offers more flexibility. However, it has some disadvantages, including lower performance and security concerns. Understanding the ISCSI architecture, protocol, and advantages and disadvantages can help you make an informed decision about whether ISCSI is the right choice for your storage needs.