IBM developed iSCSI as a proof of concept in 1998 and presented the first draft of the iSCSI standard to the Internet Engineering Task Force ( IETF) in 2000. ![]() ISCSI makes it possible to set up a shared-storage network where multiple servers and clients can access central storage resources as if the storage was a locally connected device. SCSI - without the "i" prefix - is a data access protocol that's been around since the early 1980s. It was developed by then-hard disk manufacturer Shugart Associates. ISCSI works by transporting block-level data between an iSCSI initiator on a server and an iSCSI target on a storage device. The iSCSI protocol encapsulates SCSI commands and assembles the data in packets for the TCP/IP layer. Packets are sent over the network using a point-to-point connection. Upon arrival, the iSCSI protocol disassembles the packets, separating the SCSI commands so the operating system (OS) will see the storage as if it was a locally connected SCSI device that can be formatted as usual. Today, some of iSCSI's popularity in small to midsize businesses (SMBs) has to do with the way server virtualization makes use of storage pools. In a virtualized environment, the storage pool is accessible to all the hosts within the cluster and the cluster nodes communicate with the storage pool over the network through the use of the iSCSI protocol. There are a number of iSCSI devices that enable this type of communication between client servers and storage systems. This image illustrates how a simple iSCSI SAN deployment could share the same infrastructure as the rest of the computers on the network. ![]() Ideally, however, the data and storage networks should run separately to avoid network congestion. An iSCSI initiator is a piece of software or hardware that is installed in a server to send data to and from an iSCSI-based storage array or iSCSI target. When a software initiator is used, standard Ethernet components such as network interface cards ( NICs) can be used to create the storage network. #DEFINE INITIATER SOFTWARE#īut using a software initiator along with NICs leaves virtually all of the processing burden on the servers' CPUs which will likely have an impact on the servers' performance handling other tasks.Īn iSCSI host bus adapter is similar to a Fibre Channel ( FC) HBA. ![]() It offloads much of the processing from the host system's processor, improving performance of the server and the storage network. The improvement performance, however, comes at a cost as iSCSI HBAs typically cost three or four times as much as a standard Ethernet NIC. A similar, but somewhat less expensive, alternative is an iSCSI offload engine - or iSOE - which, as its name suggests, offloads some of the process from the host. In the iSCSI configuration, the storage system is the "target." The target is essentially a server that hosts the storage resources and allows access to the storage via one or more NICs, HBAs or iSOEs. Initially, iSCSI storage systems were positioned as alternatives to the more expensive, yet higher performing Fibre Channel-based storage arrays that handled the bulk of block storage tasks in enterprise data centers.
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