G-Technology G-RACK 12, Руководство пользователя

Страница: 222 / 296

iSCSI Essentials
p. 222
Overview
In a world where Internet Protocol (IP) dominates local and wide area networks, and data storage
requirements grow unabated, it seems inevitable that these two forces converge. The Internet Small
Computer Systems Interface (iSCSI) protocol unites storage and IP networking. iSCSI enables the
transport of block-level storage traffic over IP networks. The protocol is used on servers (initiators),
storage devices (targets), and protocol transfer gateway devices. iSCSI uses standard Ethernet
switches and routers to move the data from server to storage.
What is iSCSI
iSCSI, (Internet 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.
How and when is iSCSI used?
The protocol allows clients (called initiators) to send SCSI commands (CDBs) to SCSI storage devices
(targets) on remote servers. It is a 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 some SAN protocols, iSCSI requires
no dedicated cabling; it can be run over existing IP infrastructure. As a result, iSCSI is often seen as a
low-cost alternative to Fibre Channel.
Target
The iSCSI specification refers to a storage resource located on an iSCSI server (more generally, one of
potentially many instances of iSCSI storage nodes running on that server) as a target. “iSCSI target”
should not be confused with the term “iSCSI” as the latter is a protocol and not a storage server
instance.
An iSCSI target is often a dedicated network-connected hard disk storage device, but may also be a
general-purpose computer, since as with initiators, software to provide an iSCSI target is available for
most mainstream operating systems.
Initiator
An initiator functions as an iSCSI client. An initiator typically serves the same purpose to a computer
as a SCSI bus adapter would, except that, instead of physically cabling SCSI devices (like hard drives
and tape changers), an iSCSI initiator sends SCSI commands over an IP network. An initiator falls
into two broad types. A software initiator uses code to implement iSCSI. Typically, this happens in a
kernel-resident device driver that uses the existing network card (NIC) and network stack to emulate