iSCSI which became an official standard in February of 2003, links data storage devices over an IP network and is perhaps just beginning to emerge as a serious contender in the storage industry. Why hasn't iSCSI lived up to its early hype? Who is using it today? And, most importantly, what does the future hold for iSCSI?
Getting Started: Understanding The Terminology
Storage Area Network
Storage Area Network (SAN) is a high-speed sub network of shared storage device which contains a disk or disks for storing data. In this architecture all storage devices adeed to a SAN will become accessible to all servers on a LAN or WAN or any larger network. Here the server merely acts as a pathway between the end user and the stored data. Because stored data does not reside directly on any of a network's servers, server power is used for business applications, and network capacity is released to the end user.
Internet SCSI, iSCSI is an IP-based standard for linking data storage devices over a network and transferring data by carrying SCSI commands over IP networks. iSCSI supports a Gigabit Ethernet interface at the physical layer, which allows systems supporting iSCSI interfaces to connect directly to standard Gigabit Ethernet switches and/or IP routers. Once the operating system receives a request the SCSI command is generated and then an IP packet is send over an Ethernet connection. At the receiving end, the SCSI commands are alienated from the request and the SCSI commands and data are sent to the SCSI controller and then to the SCSI storage device. iSCSI will also return a response to the request using the same protocol.
This serial data transfer architecture is developed by a consortium of computer and mass storage device manufacturers and now is being standardized by ANSI. One of the most prominent Fibre Channel standard is Fibre Channel Arbitrated Loop (FC-AL) which was designed for new mass storage devices and other peripheral devices that require very high bandwidth. Using optical fiber to connect devices, FC-AL supports full-duplex data transfer rates.
The Promise of iSCSI
The oft-repeated promise of iSCSI is relatively uniform across many storage vendors and analysts. Some of the significant differences between the two are cost differential, less complexity, implementation and maintainence in the case of iSCSI IP storage network and finally iSCSI does not scale to the same performance level as a Fibre Channel SAN.