In computing, iSCSI ( ) is Internet SCSI (Small Computer System Interface), an Internet Protocol (IP)-based storage networking standard for linking data storage facilities. By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage storage over long distances. iSCSI can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet and can enable location-independent data storage and retrieval. The protocol allows clients (called initiators) to send SCSI commands (CDBs) to SCSI storage devices (targets) on remote servers. It is a popular storage area network (SAN) protocol, allowing organizations to consolidate storage into data center storage arrays while providing hosts (such as database and web servers) with the illusion of locally-attached disks. Unlike traditional Fibre Channel, which requires special-purpose cabling, iSCSI can be run over long distances using existing network infrastructure.

Functionality

Although iSCSI can communicate with arbitrary types of SCSI devices, system administrators almost always use it to allow server computers (such as database servers) to access disk volumes on storage arrays. iSCSI SANs often have one of two objectives:

Storage consolidation

Organizations move disparate storage resources from servers around their network to central locations, often in data centers; this allows for more efficiency in the allocation of storage. In a SAN environment, a server can be allocated a new disk volume without any change to hardware or cabling.

Disaster recovery

Organizations mirror storage resources from one data center to a remote data center, which can serve as a hot standby in the event of a prolonged outage. In particular, iSCSI SANs allow entire disk arrays to be migrated across a WAN with minimal configuration changes, in effect making storage "routable" in the same manner as network traffic.

Storage area network

main: Storage area network

In the context of computer storage, a SAN system allows a machine to use a network protocol to connect to remote storage resources such as disks and tape drives on an IP network for block level input and output. From the point of view of the class drivers and application software, the devices appear as locally attached devices.

There is a difference between a SAN device and a network-attached storage (NAS) device, where computers access resources through a file-based interface rather than through a low-level device interface. A NAS server arbitrates access from multiple clients, thus allowing the arbitrary addition of consumers for its resources. With iSCSI, the burden of synchronizing access to shared resources generally belongs to the initiator (network client) rather than with the target (network server). Sharing low-level device interfaces is a requirement of computer clusters which use specialized cluster software to manage the use of shared resources.