Storage Area Networks and NT

There may be some debate over whether storage area networks (SANS) are ready for implementation. But if any company could use the aid of a SAN today it is 1-800-Database. The company maintains a central database of hundreds of thousands of product images from more than 3,000 manufacturers and captures about 2,000 new high-resolution images every day. The company faces the daunting task of backing up 1.5 TB of data from about 1.8 million files. 1-800-Database hopes a SAN will give it a better backup option. "We've been looking at SANs, but they are not quite ready to build," explains Don Otto, the company's director of technology, but the company will initiate a pilot project soon to determine SAN's promise.

Whether SANs are ready for implementation depends upon whom you ask. In New York, Fleet Securities Inc. has a SAN running with an MTI Gladiator disk array subsystem on a Fibre Channel arbitrated loop. The SAN is supporting both Unix and Windows NT servers and enables shared access to data. "I consider this a rudimentary SAN," says Marc West, vice president of infrastructure services at Fleet. The SAN, for instance, does not yet handle Fleet's Novell servers.

Most of the evidence suggests that Windows NT shops are on the threshold of SAN deployment. Hardware vendors are rapidly equipping their products with Fibre Channel connections and software vendors are racing to add SAN capabilities to their storage software tools. "You can get the SAN to work, but you have to put in a lot of effort," West concedes. Six months or a year from now, however, the picture may be completely different.

"The industry is in phase one and maybe just beginning phase two of SAN deployment," observes Scott Robinson, vice president of engineering at Datalink (, a storage-solutions provider. Phase one, he explains, consists of organizations replacing their attached SCSI disk drives and arrays with Fibre Channel counterparts.

This gives the organization greater storage bandwidth and distance as storage devices can be placed farther from the server than is possible with SCSI. Phase one, however, is not a SAN because the storage is still attached to one server.

In phase two, organizations separate the storage from the server and place it on its own subnetwork behind a hub or switch. The subnetwork may also support NT server clusters or a mixed set of servers and tape devices. Organizations can then implement a variety of failover and backup strategies. All this happens on the SAN without impacting the primary corporate network.

The industry will be moving into phase three by 2000, Robinson predicts, as SAN technology becomes mainstream. In phase three, organizations will be able to move files directly from the disk to the backup tape without having to go through a server. Organizations also will be able to initiate flexible and highly dynamic switching strategies that allow different servers to access different data depending upon the circumstances.

Blue Cross/Blue Shield of Georgia Inc. has been exploring SANs for months, but is just taking its first steps down the SAN path by decoupling its storage from its NT servers. The company is waiting for its Artecon storage hardware to sport Fibre Channel connections and for its storage management and backup software to recognize the SAN.

International Data Corp. (IDC,, predicts a fast SAN ramp up. In a recent study, titled 1998 Worldwide Fibre Channel and SAN Market Forecast and Review, IDC pegs the Fibre Channel-based NT/Unix SAN market at $550 million. IDC projects 100 percent annual growth, which will bring the market to $9.25 billion by 2002. These numbers include the value of storage arrays used in SANs. The value of switches and hubs will amount to another $2.5 billion by 2002.

Despite the powerful projections, there are a couple of catches that could cause many companies to slow their race to SANs. The big snag is interoperability. A complete SAN consists of fiber-connected disk arrays, hubs and switches, host bus adapters, tape devices, SCSI to Fibre Channel bridges and storage management and backup software. All these components have to work together.

"Hooking up a SAN is not for do-it-yourselfers. You really need somebody to take responsibility for all the pieces," says Robert Gray, IDC research manager for storage systems. Somebody needs to certify that all the pieces will work when connected to the other pieces. EMC Corp. ( is leading a pack of about 12 storage companies in an initiative to iron out the interoperability problems.

Most interoperability issues revolve around the vendors' various implementations of Fibre Channels. Compounding the problem, there is no official Fibre Channel driver for Windows NT, explains Carl Wolfston, director at Headlands Associates (, a storage systems integrator.

As a result, experts strongly advise against mixing and matching components from different vendors. "You might try [mixing and matching] in a lab, but you don't want to bet your company on the results at this point," Wolfston continues. He does, however, expect the interoperability situation to improve within the next six months.

Because of interoperability problems, many leading vendors, such as StorageTechnology Corp.(, Compaq Computer Corp., and MTI Technology Corp. ( are assembling packages of pretested SAN storage components. Smaller vendors, such as Xiotech Corp.(, are introducing what are being described as SANs-in-a-box, which include software as well as hardware. The situation, reminiscent of the early days of SCSI with its interoperability problems, will rapidly evolve toward ubiquitous plug-and-play compatibility, Gray suggests.

Less easily resolved will be the problems organizations encounter while trying fancy SAN tricks -- such as allowing any server access to any file or backing-up disks directly to tape. Here the obstacles lie with the software rather than hardware. Organizations, for example, will need sophisticated locking to control file access. But these are phase three activities; anyone fooling around with this kind of functionality right now, especially in the NT world, is playing on the edge.

The issue for most organizations today is getting started. The first step is preparation. This involves physically decoupling the storage from server, acquiring Fibre Channel-capable hardware, and implementing bridges to handle SCSI-to-Fibre-Channel conversions.

Bridges provide a fast fix, although they have limitations. SCSI-to-Fibre-Channel bridges permit bringing non-Fibre Channel capable hardware into the SAN, but there could be performance degradation. "There is enough bandwidth in the bridges to cover the throughput of tape, but you need to worry with high-speed disk," observes Dale Miller, vice president of storage at Trilliant Group (

Bridge performance problems will go away as SCSI devices are replaced. Over the next five or six years, IDC expects the demand for bridges to decline as most devices begin to incorporate Fibre Channel connections.

Once the initial steps of decoupling storage and implementing Fibre Channel are complete, an organization should then proceed in incremental stages, rather than trying to get everything onto the SAN at once.

The next step is a choice. Which comes first, disk or tape? Many organizations want to put their tape backup onto the SAN as part of an effort to centralize and streamline the process and to eliminate the need to pass huge backup files over the corporate LAN. "We are very interested in using the SAN for backup," says Bob Adair, a storage technology manager at a large brokerage firm. SAN-based centralized tape backup can produce some immediate efficiencies and savings.

Some experts suggests that tape is a good place to start a SAN initiative, if only by default. "You can put whatever you want on a SAN, but accessing a disk array with clusters and high availability is much more challenging than tape today," Miller says. Tape, he continues, doesn't have all the file system issues. Data goes onto the tape in a raw format.

"To date, backup has been the primary application driving the SAN. It is very cost effective," adds Rob Peglar, advisory engineer at StorageTek.

The tape strategy, however, isn't easy work. "We are still having trouble talking to tape drives," Adair notes. The problem is not just the fact that tape devices today don't come equipped for Fiber Channel -- such tape devices won't appear for a few more months -- but also that the current backup systems don't understand the file system, he explains. As a result, backup still needs to go through a server. Even if a company uses a bridge to connect the SCSI tape devices to the Fibre Channel fabric, it still can't back up disks directly to tape, which is the ultimate goal.

This isn't the lament of a SAN neophyte. The brokerage firm has implemented a SAN using Brocade switches, EMC and Clarion disk arrays, and Crossroads SCSI-to- Fibre-Channel bridges. It has connected Sun and Windows NT servers and their attached disk arrays in a SAN, giving the company flexibility in how it allocates disk space.

But just as the brokerage firm's experience shows the limitations of tape backup over the SAN, so it highlights the limitations of disk storage on SAN. The brokerage firm, for example, cannot allocate disk capacity to servers in a completely free manner because Windows NT is not well-behaved in the SAN environment. "We really have to keep the NT hosts from seeing the disks of other hosts," Adair explains. If not, the NT storage manager tries to grab foreign drives and overwrite partition tables.

If server data sharing is critical, Mercury Computer Systems' SANergy allows multiple servers to share data over the SAN. The product provides file locking, a requirement for any-server-to-any-disk access, but "we haven't tested it at the record level," reports Mike Hogan, technical specialist at Norstan Consulting (, a storage systems integrator.

While more needs to be done on the hardware and software ends to make SAN mainstream for Windows NT shops, organizations are beginning to effectively deploy islands of SAN and are experiencing benefits -- both for tape and disk storage. By 2000, all the pieces should come together: interconnect hardware, software, switches and hubs, Windows 2000, high-availability clusters and the fiber fabric. At that point, SAN will become as routine as SCSI disk arrays are today.

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