Mr. SAN man, send me a dream … - storage-area networks - Technology Information

Communications News, March, 1999 by Morris Edwards

Storage area networks promise to turn fantasy into reality for data-weary enterprises.

Demand for storage continues to skyrocket throughout the enterprise, threatening to clog already choked networks. In just the past 12 months, enterprise storage needs have more than doubled, according to Cambridge, Mass. research firm Forrester Research Inc.

In coping with this storage explosion, IT managers must also deal with pressure from users to provide quick and reliable access to mission-critical data that is often scattered among many different platforms. To meet the challenge, a growing number are embracing new concepts and enabling technologies such as network-attached storage, storage area networks, and Fibre Channel.

POOLED RESOURCES

Network-attached storage (NAS) devices enhance performance and simplify management and administration by using a dedicated server in place of the traditional Windows NT, Unix, or NetWare application server.

These general-purpose servers are ill equipped for handling files because they have full operating system kernels and lack specialized coprocessors for storage and communications functions. In contrast, an NAS server uses a proprietary operating system, optimized for I/O and simplified administration. Essentially, you simply plug the server into your network, assign it an address, and let other servers know it's there, at which point you have a shared-storage pool available to all users as a network resource. To applications running on the network, it looks like an ordinary server; to any client, it looks like a large hard disk.

Even with network-attached storage, though, performance can deteriorate markedly if the server becomes overloaded. That's why there's growing interest in the idea of linking servers and storage devices with a network of hubs and switches.

By eliminating the islands of data dedicated to single servers, storage area networks (SANs) promise to make more data available to more users more quickly than ever before while simplifying the expansion, administration, and management of data storage. More than two-thirds of large-company data administrators responding to a Forrester Research survey said they were considering implementing SANs within the next 12 months. According to Strategic Research, Santa Barbara, Calif., the SAN market for hardware, software, and services will grow from an estimated $3.5 billion in 1998 to $14.8 billion by 2000.

With a SAN, storage devices are shared among all network servers as peer resources. Different kinds of storage can be shared by various servers, including Windows NT, Unix, and NetWare devices, enabling users with heterogeneous storage platforms to utilize all their storage resources.

Servers can connect to storage or to each other, and you can have direct storage-to-storage links. This means that users can back up or archive data from different disks to a common tape without going through a server or interfering with ongoing data access. Users can also automatically create and store a mirror image of data to another disk-possibly a remote one for greater security and disaster recovery.

Besides improving security, availability, and scalability, SANs provide a single point of administration, allowing storage to be managed as a single entity rather than server by server. SAN downtime, however, is a critical issue; and the major enterprise network management vendors are busy beefing up their storage management capabilities and integrating them into their framework platforms.

ENERGIZING STANDARD

As do other networks, SANs can support multiple transport technologies and a number of protocols, including TCP/IP. Interoperability remains an issue. Hoping to remove this roadblock, several major storage vendors have formed the Storage Networking Industry Association to promote new technologies and develop standards. Individual suppliers are also seeking to make their products interoperable with those from leading vendors.

In a sign of progress, Veritas Software Corp., Mountain View, Calif., recently put together a SAN with products from more than a dozen vendors. Veritas used a networked collection of Windows NT, HP-UX, and Solaris-based servers, hooked up to storage arrays and tape libraries, to demonstrate the latest versions of its Storage Manager and Cluster Server in support of a high-availability version of SAP R/3 on Oracle databases. The software, which runs on Windows NT and other popular platforms, includes a Java-based graphical user interface for centralized monitoring and management of all devices on a SAN.

One standard that has energized SANs is the Fibre-Channel specification developed by the American National Standards Institute's X3T11 committee as a faster way to transfer data between servers and storage devices than its SCSI (small computer systems interface) predecessor. Whereas the fastest SCSI channel operates at 40 Mbps, Fibre Channel speeds can top 100 Mbps.

What equips Fibre Channel for SANs is its support of multiple protocols and network topologies and its ability to handle up to 127 devices on a single loop over much greater distances than SCSI's limit of 25 meters. With single-mode fiber, Fibre Channel extends the range to 10 km, making it suitable for campus SANs and allowing remote mirroring for disaster recovery.