iSCSI

In the context of computer storage, Internet SCSI (iSCSI) is an official standard ratified on February 11 2003 by the Internet Engineering Task Force, uses the SCSI protocol over a TCP/IP network. It enables any machine on an IP network (initiator) to contact a remote dedicated server (target) and perform block I/O on it just as it would do with a local hard disk.

Functionality

The iSCSI protocol uses TCP/IP for its data transfer. Unlike other network storage protocols, such as Fibre Channel (which is the foundation of most SANs), it requires only the simple and ubiquitous Ethernet interface (or any other TCP/IP-capable network) to operate. This enables low-cost centralization of storage without all of the usual expense and incompatibility normally associated with Fibre Channel storage area networks.

Critics of iSCSI expect worse performance than Fibre Channel due to the protocol overhead TCP/IP adds to the communication between client and storage. However new techniques like TCP Offload Engine (TOE) help in reducing this overhead. And tests have shown excellent performance of iSCSI SANs, whether TOEs or plain Gigabit Ethernet NICs were used. In fact, in modern high-performance servers, a plain NIC with efficient network driver code can outperform a TOE card because fewer interrupts and DMA memory transfers are required. Initial iSCSI solutions are based on software stack. The iSCSI market is growing steadily, and should improve in performance and usability as more organizations deploy Gigabit and 10 Gigabit networks, and manufacturers integrate iSCSI support into their operating systems, SAN products and storage subsystems.

Industry support

Initiators

OS Support Overview

OS	Date	Release
AIX	10/2002	AIX 5.2
Windows	06/2003	2000, XP Pro, 2003
NetWare	08/2003	NetWare 6.5
HP-UX	10/2003	HP 11i v1, HP 11i v2
Solaris	02/2005	Solaris 10
Linux kernel	06/2005	2.6.12

Initiator Implementations

Adaptec is shipping a TOE NIC
Cisco has a free software initiator for most Operating Systems
IBM AIX since version 5.2 (October 2002)
HP iSCSI Software Initiator
Intel has funded an open source initiator
Linux:
- Projects: Open-iSCSI, Linux-iSCSI merged in April 2005 with Open-iSCSI project
- Included in Vanilla kernel since version 2.6.12 (17 June 2005)
Solaris iSCSI initiator, since Solaris 10 (February 2005)
Microsoft announced its support for iSCSI by providing iSCSI inititators in their latest Windows OS and storage server products: Windows 2000, Windows XP Professional and Windows Server 2003
Novell provides an iSCSI initiator for its NetWare operating system free of charge.
PyX Technologies licenses the complete iSCSI protocol software, (including all error recovery levels, mandatory and optional feature sets), to OEMs, developers and integrators.

Targets

ATTO Technology offers iSCSI to SCSI and iSCSI to Fibre Channel bridges
Cisco bridge
EMC Corporation
EqualLogic offers a storage array that can handle iSCSI traffic from NetWare, Windows, Linux, Solaris and is the leader in the dedicated IP SAN Market
FalconStor offers Enterprise Integrated IP/iSCSI/Fibre Channel SAN
HDS
HP has a complete set of storage products/services ranging from Small to Enterprise SANs
IBM
Linux Open Source: iSCSI Enterprise Target, UNH-iSCSI
Network Appliance Filers
Intransa offers enterprise-class iSCSI based IP SAN.
Novell NetWare 6.5 includes iSCSI target software.
PyX Technologies offers a storage engine that can export out any type of storage as iSCSI
SANRAD offers an all-in-one iSCSI based IP SAN.
StoneFly Networks offers IP SANs for departments, workgroups and mid-tier organizations
Stringbean Software offers WinTarget a Windows iSCSI target software.
Voltaire Inc. offers iSCSI/iSER based InfiniBand to Fibre-Channel Routers.

External links

RFCs

RFC 3720 - Internet Small Computer Systems Interface (iSCSI)
RFC 3783 - Small Computer Systems Interface (SCSI) Command Ordering Considerations with iSCSI