Glossary: Commonly used iSCSI Terms

Array- A collection of hard drives that represents itself to the computer as one drive.

Cluster- This refers to a number of different implementations of shared computing resources. Typically, a cluster integrates the resources of two or more computing devices (that could otherwise function separately) together for a common purpose.

Ethernet- A physical and data link layer technology for local area networks (LANs).

Gigabit Ethernet- Packet-based signaling technology that transmits data at throughput speeds up to 1000 megabits per second (Mbps), or 1 Gigabit per second (Gbps). Many Gigabit Ethernet components are backward compatible with Ethernet (10 Mbps) and Fast Ethernet (100 Mbps).

Initiator- A device that begins an iSCSI transaction by issuing a command to another device (the iSCSI target), giving it a task to perform. Typically an iSCSI host adapter is the initiator but targets may also become initiators.

iSCSI [Internet Small Computer Systems Interface]- A protocol that maps SCSI onto the TCP (transmission control protocol) in order to allow storage links to be extended greater distances over IP networks.

SAN [Storage Area Network]- A high performance network or subnetwork designed to connect storage elements and the back end of the servers. A typical application of SAN is network data storage.

Storage Target- An iSCSI device that executes a command from an iSCSI initiator to perform some task. Typically the target is an iSCSI storage device but the host adapter can also be a target.

Switch- A network communications device that routes packets (messages or fragments of messages) between nodes across virtual circuits.

TOE (TCP Offload Engine)- TOE technology shifts TCP packet processing tasks from the server CPU to specialized TCP processors on the network adapter or storage device. TCP Offload Engines address the increasing demand put on servers by Gigabit connections and are particularly useful with iSCSI and the transport of block-based storage data over Gigabit Ethernet networks. In IP storage communications, packet processing can significantly load the CPU, reducing the CPU’s ability to run applications or maximize data throughput. By offloading packet processing on a TOE, the CPU is free to run its applications without repeated interrupts, so users get their data faster.