iSCSI Glossary

This article introduces some key terms used in iSCSI to help you better understand and use iSCSI.

1. iSCSI

iSCSI (Internet Small Computer System Interface) is an IP-based storage protocol. It allows users to remotely access and manage storage devices over a standard Ethernet network as if they were directly connected to the local computer. In practice, data written to the disk is transmitted over the network to the storage server (NAS).

2. LUN

A LUN (Logical Unit Number) represents an addressable SCSI logical device, essentially a virtual hard drive. You can specify the size and the volume for a LUN. Once configured, it can be mounted and used for data read/write by client computers.

3. Thick and Thin Provisioning

A Thick provisioned LUN allocates the specified capacity from the volume all at once upon creation. It offers stable performance with lower system latency.

A Thin provisioned LUN allocates only a small amount of space upon creation and dynamically expands as data is actually written. It provides higher storage utilization.

For performance reasons, the minimum LUN size is 5 GB regardless of the provisioning mode.

4. Target

A Target is an access endpoint provided by the NAS. Client computers connect to LUNs through a Target. Targets support password protection (CHAP) for enhanced security.

5. IQN

An IQN (iSCSI Qualified Name) is a name used in iSCSI to uniquely identify client computers and Targets. It follows a specific naming format.

Think of it as a unique identifier for both clients and Targets.

6. Initiator

An Initiator is the client-side program that runs on a computer (Windows, Mac) and sends connection requests to a Target on the NAS using an IQN.

Windows has a built-in iSCSI Initiator and does not require separate installation. macOS does not natively support iSCSI and requires third-party tools (such as DAEMON Tools).

7. User Group

You can add the IQNs of Initiators from different devices to the same user group, and then batch-configure LUN read/write access permissions for Initiators through the user group.

8. CHAP

CHAP (Challenge-Handshake Authentication Protocol) is a password-based authentication mechanism that prevents unauthorized access. It supports two modes: one-way and mutual.

One-way CHAP: Only the Initiator authenticates the Target.

Mutual CHAP: The Initiator authenticates the Target, and the Target also authenticates the Initiator.