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How advanced iSCSI architectures can extend the functionality of SATA for IP storage. (Tape/Disk/Optical Storage).

The disk storage market is expected to reach $29 billion in annual revenues by 2005. At the same time, prevailing architectures like Fibre Channel SANs and Gigabit Ethernet NAS (network-attached storage) are reaching their limitations. However, a new protocol called iSCSI (SCSI over TCP/IP)--long endorsed by such companies as Intel, IBM, Dell, Hitachi Data Systems, Cisco, Emulex, QLogic, Maxtor, Seagate, and Western Digital--positions IP storage as the emerging solution that promises to solve many of the limitations that impact conventional storage networking.

iSCSI, in fact, has officially arrived. On February 10, 2003, the Internet Engineering Task Force (IEFT) formally ratified the iSCSI specification, enabling IP storage to be adopted by storage vendors and their customers. iSCSI facilitates data transfers over Intranets and manages storage over long distances by carrying SCSI commands over IP networks, therefore reducing the cost of shared storage solutions and of unifying disparate systems and data.

Of the many iSCSI devices to be announced this year, most will be low-end appliance-like devices, ideal for companies looking to move away from direct-attached storage and reap the benefits of a storage network without needing a dedicated support staff.

By the end of 2003, nearly every operating system will support the iSCSI standard. Microsoft has announced native iSCSI support in its Windows.NET Server 2003 as well as Windows 2000. IBM, Cisco Systems and Network Appliance will also be announcing new iSCSI solutions, and Intel's LAN division plans to make iSCSI a standard part of every server it ships. IDC, a leading technology industry analyst firm, predicts that by 2008 most storage networking interfaces deployed will be IP-based.

On the customer side, companies are determining the types of applications best suited for iSCSI. Starting with e-mail, database, file, and print applications, enterprise customers will use iSCSI for business continuance applications. iSCSI leverages the IP backbones and enterprise networks already in place with midrange and low-end servers, using primarily server-based replication software. By the end of 2003, iSCSI will be the preferred choice for many small to medium-sized businesses.

Other new technologies, coupled with iSCSI, are also going to play a large role in storage. Because of the inherent physical limitations of parallel interfaces, inexpensive or cost-effective serial interfaces like 10- and 40-Gigabit Ethernet, SATA and 3GIO (PCI Express) are poised to be part of this flourishing future for IP storage. Disk drive manufacturers are already starting to deliver enterprise-level devices with SATA interfaces that provide 10,000 RPM, 1.2 million hours MTBF, 5.2-millisecond seek time, and five-year warranties, at prices 30% lower than traditional SCSI drives.

However, SATA interfaces have limitations as well--mainly, the number of drives that a chip component can address. For example, Marvell Technology is shipping a PCI-X chip with eight SATA ports--each port connecting to a disk drive. Accordingly, an average storage controller using two such chips can support only 16 SATA drives. The inability to go beyond 16 SATA devices per controller has been a major roadblock to the scaling up of SATA storage in a cost-effective manner because the controller cost is spread across only 16 drives.

Another limitation of the SATA interface is its mere one-meter cable length. This presents a drawback for SATA storage in terms of scaling outside the box. The challenge is how to match the 10-km range of a Fibre Channel interface.

Scaling Up and Scaling Out

In a perfect world, iSCSI products would be viewed as part of a complete IP storage networking solution--for server, storage, and networking OEMs-- that could coexist in the data center with Fibre Channel and other technologies. The world may not yet be perfect, but new technologies and iSCSI devices are on the near horizon that would foster this coexistence, while enabling enterprise storage OEMs to expand the number of drives a single controller can accommodate plus address the cable length challenge as well.

In terms of iSCSI devices, there are two sides to the equation: the "initiator" side" and the "target" side. On the initiator side are host devices (such as file servers) that exchange block data with target-side devices (disk arrays, tape libraries, etc.) over the IP network via storage routers, switches, and other kinds of networking equipment. Although there already are plenty of iSCSI initiators, there are still scant few native iSCSI target-side devices, which are necessary to take IP storage to the next level. Slowly but surely, though, things are starting to change on the target side, with the introduction of such devices as a scalable 10Gb/sec full wire-rate iSCSI storage server blade that promises to fulfill internal and external networked storage requirements.

For target-side devices like this to provide an efficient, performance-oriented IP-based SAN solution, they would need functionality like TCP/IP and iSCSI off-load and such high availability features as redundant mirror channel at zero latency, and an RDMA (remote direct memory access) capability. Additionally, enterprise-level devices require an architecture that can aggregate multiple 1GbE iSCSI ports to--in effect--allow as many as 128 SATA drives in the same storage domain for more than 30 terabytes of data storage pooling and provisioning. While still only 16 SATA drives per controller would be used, this technology would allow for more relatively inexpensive 2-port "expansion" controllers to be connected to an 8-port, fully redundant iSCSI-to-SATA "command" controller using standard switches, which would give the impression that all drives were connected to a single command controller. In essence, this hierarchical architecture would spread put the cost of controllers, resulting in a better cost/capacit y ratio and a much lower TCO (total cost of ownership).

With this type of architecture, OEMs could offer cost-effective entry-level solutions with scalability--accomplished by limiting the number of front-end iSCSI ports and the number of back-end SATA connections. It would also enable much higher-end solutions utilizing all eight 1-GbE iSCSI front ends and an iSCSI expansion technology that addresses hundreds of SATA drives--and without having to wait for new expansion technologies currently being developed. Finally, it would allow OEMs to offer a wider range of iSCSI solutions to their customers while greatly reducing the need for additional engineering development that would directly impact product cost.

The dual-active configuration environment of this kind of architecture would feature two storage server blades, each with up to eight 1-GbE ports or a single 10-GbE port on the front end. The back-end interface would be agnostic and, today, would support SATA. However, using the same storage server blade with minor hardware and firmware changes, it could also support Fibre Channel or Ethernet. This is important because Ethernet is ubiquitous; everyone has it, all the IT and MIS people know how to work with it, and it's very cost-effective in terms of installation, maintenance and serviceability.

From that one interface, the cable length could be extended up to 10 kilometers and, with the expansion controllers, to as many as 16 SATA drives per expansion enclosure. With up to eight expansion enclosures, scaling up to 128 SATA drives--and a capacity of 30 terabytes--this would provide an affordable solution for primary storage, fixed content storage, content addressable storage, disk-to-disk backup, and other applications.

Meeting Market Requirements

Although advanced new target-side iSCSI devices and architectures can indeed lift IP storage to the next level, they are very difficult to develop for meeting the requirements of effective scaling up and scaling out. Taking a conventional Fibre Channel-like approach by integrating single or dual embedded processors with network layered protocols can no longer meet the stringent market demands for better performance, scalability, and dual-active redundancy--as well as cost effectiveness. Therefore, new iSCSI target-side devices--such as iStor's iBlade storage server blade which embeds a dozen specialized processors and super-fast state machines in breakthrough architecture to create scalable front-end and back-end interfaces--will be the secret to success on the target side. Achievement, however, presents a formidable challenge because implementation would require the vendor to have core competencies not only in storage and network technologies but also in ASIC design and massive parallel processing architectu re.


With the emergence of iSCSI, SATA and other serial interfaces, IP storage is dramatically proliferating in the desktop, server, data center, and distributed environments. At the same time, new technologies, architectures and devices promise to enable server, storage and networking OEMs to deliver cutting-edge, value-added storage-networking features such as link aggregation, quality of service, high availability, volume virtualization, and extensible scalability to expand the cost advantage of iSCSI and SATA interfaces.

Simon Huang is president and CEO of iStor Networks, Inc. (Irvine, Calif.)
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Article Details
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Author:Huang, Simon
Publication:Computer Technology Review
Date:Jun 1, 2003
Previous Article:Disk-to-disk backup: pass the data please. (Tape/Disk/Optical Storage).
Next Article:Roundtable: "switched on storage arrays" Part 1 of 3. (Tape/Disk/Optical Storage).

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