August 2001
iSCSI Sets A New Standard for SANs
by Lowell Rapaport
In an era of rapidly expanding storage demands and increasingly distributed enterprises, storage area networks (SANs) have emerged as the most flexible, scalable way to meet big-league storage demands. The trouble is, SANs are expensive: Up until now they've been built on fibre channel hardware that can cost as much as $1,000 per port.
Enter iSCSI, a new approach to building SANs due to be adopted as a standard by the fourth quarter of 2001. Promoted by such heavy hitters as Cicso and IBM (see "Cisco and IBM Forge Ahead," page 46), iSCSI replaces fibre channel's tightly integrated hardware and software network protocol with a software protocol, TCP/IP, which can be carried by a wider variety of networking hardware.
Combining existing hardware, lower-cost networking components and easily understood Internet protocols, iSCSI is expected to make SANs affordable even for smaller enterprises. iSCSI has yet to prove itself, with standardization work and testing still in progress, but for those contemplating or building SANs today, the technology demands consideration.
How iSCSI Works
iSCSI isn't complicated: It wraps SCSI commands inside Internet protocol (IP) packets. In theory, the technique is similar to that used by fibre channel, where SCSI commands are wrapped inside fibre channel frames. IP networking, however, is more well known and functions on a wider variety of networking hardware, including ordinary Ethernet local area networks (LANs), corporate wide area networks (WANs) and the Internet.
Any network capable of supporting IP can be pressed into service for iSCSI, including asynchronous transfer mode (ATM) or frame relay connections (two of the most popular protocols for corporate WANs), optical carrier or leased T1 or T3 digital lines or even digital subscriber lines (DSL).
One of the only genuinely new hardware items needed for iSCSI SANs is a network interface card (NIC), which can extract the SCSI commands from incoming IP packets for the storage devices. This special NIC needs no software or general-purpose CPU and no hard drives or interfaces other than Ethernet and SCSI, making it the thinnest of thin servers.
Storage devices equipped with NICs are called IP storage; they are equipped with just enough electronics to get on a network and communicate with a server. Features commonly found on network-attached storage (NAS) devices - file and user management, security and a Web or FTP interface - are absent from IP storage. Instead, the relationship between a server and IP storage is exactly the same as with traditional server-attached storage; the only difference is that the devices are connected to each other over the network.
Just as with conventional server-attached storage, the server takes on the responsibilities of user and file management. Hard drives and RAID systems are formatted using the server's native disk format, while optical jukeboxes and tape libraries are managed by library management systems.
Development Milestones
Before SANs offering all these advantages can be deployed, the iSCSI standard has to be adopted by the Internet Engineering Task Force (www.ietf.org), the advisory committee that recommends standards for the Internet and its technologies. Only then can advances, including iSCSI NICs (for storage devices) and accelerated Ethernet cards (for servers), be introduced. (Servers can be connected with conventional Ethernet cards, but vendors are already developing accelerated Ethernet cards designed to improve server performance.)
According to Jonathan Hubert, vice president of marketing at iSCSI vendor Netconvergence, Santa Clara, CA, there is a good chance that iSCSI Version 1.0 will be finalized by October 2001.
"We expect to have software iSCSI drivers available in the third quarter and accelerated Ethernet cards in the fourth quarter," says Hubert, whose company is participating in the IETF review process. "Realistically, iSCSI devices should start shipping in quantity in the first quarter of 2002."
Even if the equipment becomes available on this schedule, "it will be 12 to 24 months before iSCSI gets widely adopted," contends Parsa Rohani, vice president of marketing and strategic planning at Procom, an Irvine, CA-based maker of NAS and SAN systems.
Rohani says that accelerated Ethernet cards will have to incorporate special processors to maintain a TCP/IP stack. "iSCSI has been demonstrated with regular [Ethernet cards] using the server's CPU to do the work of encapsulating SCSI commands in IP packets, but it's a processor-intensive task and very slow," he explains. "Early iSCSI shipments will mainly familiarize developers and users with the protocol while the hardware matures."
Neither Hubert nor Rohani believe that cost will be a limiting factor in the adoption of iSCSI. "Because iSCSI is based on Ethernet technology, it can be deployed on both clients and servers," says Rohani. "The high volume required for client-side installation of accelerated Ethernet cards should bring costs down."
While accelerated Ethernet cards may not reach the commodity prices of conventional Ethernet ports (which now sell for less than $20 each), Rohani predicts costs could fall below "a few hundred dollars per port" within a year. This figure is less than (though not much less than) fibre channel's price range of $500 to $1,000 per port. In addition, iSCSI SANs can use existing Ethernet routers and hubs, while fibre channel requires special hardware throughout.
Potential iSCSI Roadblocks
Citing questions about iSCSI performance, some storage vendors are less enthusiastic about iSCSI. "It remains to be seen how much performance we'll get out of iSCSI systems in real-world applications," comments Russ Ritchie, director of product marketing at MTI, a RAID and SAN equipment maker in Anaheim, CA. "It will be at least 12 months before iSCSI will be competitive with fibre channel in terms of performance and latency. If the price of iSCSI-capable ports remains high, most users will not want to install them on every client in an enterprise."
Most client computers don't need high-speed access to centralized storage, Ritchie points out, and he adds that most of a SAN's cost is in management, not hardware.
"SAN hardware accounts for about a third of system costs," Ritchie explains. "Cutting hardware costs [by choosing iSCSI over fibre channel] saves only a small fraction of total system costs." Despite these reservations, Ritchie acknowledges that MTI will probably add iSCSI to its list of connectivity options.
Another potential pitfall for iSCSI users is that it requires high-quality network service. "Except for in-house corporate LANs and WANs, IP networks don't usually have the same quality of service you get with fibre channel," says Michael Del Rosso, chief technology officer of OTG, Rockville, MD. IP networks are usually designed for general-purpose networking, not for storage infrastructure. Those who plan to rely on commercial network bandwidth to support a SAN must ensure that it is up to the task.
Adding a historical perspective, Eric Ottem of Gadzoox Networks, a SAN equipment provider in San Jose, CA, reflects, "Both fibre channel and SCSI took seven to eight years development each before they were ready for widespread deployment. iSCSI has just three years development behind it and is five years behind fibre channel."
Gadzoox is heavily invested in fibre channel, and Ottem, the company's senior director of product marketing, believes performance, quality of service and cost issues with IP networks have to be solved before iSCSI will be a serious contender in enterprise storage networks. "These are engineering issues and are solvable ... but it will take time. Still," he acknowledges, "there is the possibility that iSCSI will replace fibre channel for most storage network architectures within about five years' time."
If iSCSI can truly replace fibre channel, SANs may change from being exotic, high-end storage solutions to systems that can be deployed at all but the smallest organizations. iSCSI can also encompass a much wider variety of storage devices, including magneto-optical and low-end CD/DVD jukeboxes. If the rosiest predictions for iSCSI come true, the technology may turn out to be the preferred method of adding storage to networks and transform SANs into mainstream storage infrastructures.
Why SANs Make Sense
SANs allow enterprises to easily scale up their storage infrastructure as their needs grow. Additional servers and storage can be added to a SAN without disturbing continuing operations. The SAN's ability to pool resources and then repartition them allows storage to be centralized for easy management while serving the needs of many departments. With a SAN, every department in an enterprise, however small, can take advantage of the enterprise's full storage resources.
To enable SANs, networking technology that was as flexible as traditional LANs and as fast as a direct SCSI connection had to be perfected. As a result, most SANs are currently put together using fibre channel. Fibre channel is fast at 100 MB per second per channel, and there is a full range of networking gear available, including routers, hubs and switches.
Despite these attractions, fibre channel hardware is expensive at $500 to $1,000 per port. iSCSI, in contrast, demands only special NICs for storage devices and accelerated Ethernet cards for servers. The technology leverages existing TCP/IP-compatible networks as well as conventional hubs, switches and routers (see main article). -LR
Cisco and IBM Forge Ahead
While the iSCSI standard is still a few months away, products based on the technology are already available. IBM, Armonk, NY, was first out of the gate with its IP Storage 200i. This device is a network-attached RAID storage system ranging from 108 GBs to 1.74 TBs and priced from $20,000 to $100,000, depending on capacity.
The IP Storage 200i is designed for LANs. In the absence of iSCSI NICs (which have yet to be standardized), the device employs a Linux-based Pentium III computer. "The Linux server creates virtual, block-level access to a pool of storage on the appliance," explains Jim Tuckwell, an IBM storage marketing manager. "This makes the IP Storage 200i more extensible on the back end." Tuckwell adds that 14 drive-bay enclosures can be added to the system to scale storage to the terabyte level.
Connected to a server via gigabit Ethernet, the IP Storage 200i provides a replacement for RAID and JBOD systems without the complexities of setting up SCSI channels to the server. Administrators can set up servers and connect to the IP Storage 200i with Ethernet. Additional software installed on the server, such as Tivoli's shared file system, can let multiple servers share the same storage device in a true SAN configuration.
Cisco has introduced yet another iSCSI device. The company's SN 5420 Storage Router could more appropriately be called a gateway since it combines the functions of a bridge, by converting from Ethernet to fibre channel, and a router, by performing network address translation. Priced at $27,000, the primary market for the SN 5420 will be to connect SANs located at various points around the country via existing IP infrastructure.
"We see a lot of demand for backing up over IP networks across long distances," says Mark Cree, general manager of Cisco's storage router business unit.
In the rarefied environment of connecting remote data centers together, companies could make do with proprietary solutions built on optical fibre or digital phone lines. However, most companies prefer to work with nonproprietary solutions such as iSCSI. -LR
Software Vendors Are Ready for iSCSI
SANs and storage management software integrate through drivers, so it understandable that storage software vendors are as happy with iSCSI as they are with fibre channel or traditional server-attached SCSI.
"Our software will work just as well using iSCSI protocols as with any other," says Kamel Shaath, chief technology officer for KOM Networks, Kanata, Ontario. "For IT managers, iSCSI has advantages. Internet protocol is well understood, and there are many tools available for managing IP networks. This should make it relatively easy to set up iSCSI devices."
IP networks are not only familiar, they are also easier to work with than fibre channel says Michael Del Rosso, chief technology officer of OTG, Rockville, MD. "There are things you'd like to do with storage that are hard to do with back-end protocols [like fibre channel] that are easy to do with front-end protocols [like TCP/IP]," Del Rosso explains. "Multipoint broadcasting, for example, is useful for when you want to mirror storage devices."
TCP/IP has long supported broadcasting packets to multiple devices at once. Putting SCSI commands inside TCP/IP packets lets you send the same SCSI commands to multiple devices simultaneously. This functionality is a plus for companies that need to maintain high availability by mirroring storage centers across the country. Also, because iSCSI makes use of conventional networking hardware, iSCSI networks have no physical distance limitations. Fibre channel has a range limit of 6.2 miles without repeaters, which means that long-distance fibre channel connections have to be made on special transmission lines. iSCSI connections, in contrast, can use ordinary, leased commercial networks.
iSCSI has advantages within the LAN as well, particularly for content management users. For example, in a typical archiving application, content is stored on tape or optical libraries connected to servers running library management software. To improve scalability, library management systems allow multiple servers to be networked, all sharing a single database that controls access to the archived files.
iSCSI permits fundamental changes in the architecture of library archives. Instead of attaching each library to a separate server, the libraries can be directly connected to an IP network with iSCSI-enabled network ports to a SAN. The access load for each physical library is shared among the servers connected to the iSCSI SAN. The database managing the archived files is likewise no longer restricted to a single gateway machine; it can also be shared among all the servers in this SAN. The software to accomplish this setup is available from both OTG and KOM Networks. With archival storage no longer tied to a server, it's easier to scale up. -LR
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