As the demand for data storage in client-server computing environments continues to grow, there is an increasing need to effectively manage and direct the growth of storage resources. A particularly attractive solution to this problem involves pooling storage resources and enabling access to the pool by a variety of servers. This model can be implemented as a storage area network, or SAN, as shown in Figure 1. In SANs, storage resources are interconnected with numerous servers using interconnect devices analogous to those used in LAN environments (switches, hubs, etc.). SAN environments provide "any-to-any" communication between servers and storage resources. In addition, it is possible to have multiple paths from any single server to any single storage device, as well as paths directly between storage devices.

SANs provide many potential advantages over other storage configurations. For example, in data warehousing or Internet service provider applications, multiple servers can access the same database. If one server is slow or unavailable, access can be made available through another server. Because it is possible to establish communication directly between storage devices, data can be mirrored through direct disk-to-disk connections to make multiple copies of data available. One can also perform direct disk-to-tape backups that execute with minimal server involvement. Redundant connections from servers to storage devices make SANs ideal for high availability environments. All these benefits are realized at the same time that network traffic over the LAN is decreased. This is also an advantage that SANs have over network attached storage: the heavy storage-server traffic is removed from the LAN, freeing up bandwidth for client-server traffic.

In addition to these advantages, the management of growth is also greatly simplified. When more storage is required, it is not necessary to connect a new disk to a specific server. One only has to add it to the pool. New servers can be added with similar simplicity. Essentially, SANs allow storage to be managed as a single entity rather than on a server-by-server basis. Managing a single pool of storage resources is significantly easier than trying to manage the storage for tens or even hundreds of servers.

Today, SANs are generally implemented in homogeneous operating system environments, usually UNIX. However, as SAN technology develops, one can expect to see them implemented in environments with mixtures of operating systems, including Microsoft Windows NT. Eventually, SANs will not only support UNIX and NT, but will also be interfaced to legacy mainframe environments to provide access to data that cannot be cost-effectively moved into today’s client/server environments.

As SAN technology continues to develop, more sophisticated implementations will be realized. Switches and other controllable components will allow SANs to be reconfigured "on the fly." For example, it will be possible to implement self-repairing systems in which management programs can automatically reconfigure the SAN to bypass communication line faults. It will also be possible to reconfigure the SAN as demands for data change by making additional data paths available.

Ultimately, it will be possible to implement a self-managing SAN in which the configuration adjusts dynamically to achieve pre-defined service-level objectives. This concept is called policy-based SAN management. As an example, consider a system in which data paths are dynamically added or removed in an effort to achieve a minimum wait time for all data requesters. Such a system could also automatically distribute data over the different storage devices in a SAN in a way that minimizes access time.

Today, SANs are most commonly implemented using Fibre Channel. Developed in the late 1980s by the American National Standards Institute, (ANSI), Fibre Channel was designed to move large volumes of data very quickly. Fibre Channel can be implemented with twisted pair, coaxial cable, or fiber optic cable. It supports a number of protocols, including SCSI, the most common protocol used to communicate between servers and storage devices.

However, Fibre Channel provides a number of benefits over SCSI (even the latest variation, Ultra SCSI). The connectivity and distance characteristics of Fibre Channel enable far more complex server/storage configurations than are possible with SCSI implementations. Specifically:

• Distances between devices can be as great as 10 km.
• Various network topologies are possible, including point-to-point, arbitrated loop, and switched network, or fabric.
• Fibre Channel can transfer data at speeds up to 100 Mbyte/sec (200 Mbyte in full duplex mode) depending on the cabling media.

Finally, Fibre Channel represents a significant improvement over SCSI with its smaller, more reliable connector and thinner, less expensive cabling.

One of the first Fibre Channel devices to enter the market was the Fibre Channel to SCSI bridge or multiplexer (MUX). This device enables the connection of several SCSI devices to a server through one Fibre Channel port called a host bus adapter, or HBA. An obvious use for a bridge is to conserve I/O ports in the server; several SCSI devices can be interfaced with the server using only a single I/O port. A typical application involves multiple tape libraries connected to the bridge via SCSI. The higher speed of the Fibre Channel connection enables faster backups as data is multiplexed between tape drives. Bridges also provide investment protection, extending the useful life of SCSI devices in a Fibre Channel environment. Furthermore, because of the increased distance characteristics of Fibre Channel, it is possible to place tape libraries in secure locations at some distance from the servers, providing enhanced disaster recovery capability.

More recently, several manufacturers have introduced Fibre Channel hubs to the market. These devices enable the creation of Arbitrated Loop topologies, analogous to Token Ring or FDDI LAN topologies. Hubs facilitate loop implementation by aggregating loop ports in a physical ring configuration. Hubs typically provide 7 to 12 ports and can be used to build larger loops by cascading hubs. The hubs enhance the reliability of the loop configurations by providing bypass circuitry at each port that keeps nonfunctional devices from disrupting loop traffic.

Arbitrated Loop configurations enable direct device-to-device communication making true serverless backup possible. In addition, multiple servers and multiple storage devices can be interconnected to enable file sharing and redundant system configurations for high-availability applications. Using Arbitrated Loop topology, one of the node addresses is reserved for a Fibre Channel switch. When implemented, a switch enables the loop to participate in larger networks or fabrics with multiple switches and loops. Some manufacturers offer a switching hub that manages two or more Arbitrated Loop configurations to create a larger, logical loop. This functionality offers some of the advantages of a Fibre Channel switch at a lower cost.

The latest Fibre Channel interconnect devices to enter the market are full switches. A typical switch has 8 to 16 ports and is programmatically configurable to allow the interconnection between servers and storage devices to be dynamically changed. The per-port costs for switches are usually significantly higher than the per-port cost for hubs because a switch requires processing power, memory and programming capability at each port for configuration purposes. Using switches it is possible to provide additional pathways between servers and data storage devices in response to changing user demands or to provide alternate pathways in the event of device faults. It is also possible to interconnect switches and hubs thereby creating very complex SAN configurations.

What are the "missing ingredients" that will enable the widespread adoption of SANs?

Probably the most obvious and pressing need is for management software. A SAN doesn’t have to be very complex before it becomes difficult to manage. While many Fibre Channel devices are supplied with device-specific software to manage their own functions, there is currently no software available to manage the entire SAN. Today, each SAN implementation must be supported by custom software written for its specific environment.

In addition SAN technology will not reach its full potential without operating system enhancements. To effectively share disk space between servers, the operating system must have a distributed file system and an effective file locking mechanism in place. File sharing requires even more changes to the operating system. Most system suppliers are already in the process of making modifications to their operating systems to support SAN technology. However, SAN technology offers many benefits that can be realized with current releases of operating systems. Examples include serverless backup and the simple implementation of redundant systems for high availability applications.

Another roadblock to the widespread adoption of SAN technology is the lack of software interface standards. While the Fibre Channel standard itself is well established, there are no standards to address the control or management of devices. Each device manufacturer is free to define its own management interface. This implies that management software must be written to support each manufacturer’s management interface. While this may be possible in early stages of SAN development, this situation cannot continue as more and more manufacturers introduce products into this market. Efforts to define standards are currently being undertaken by the Storage Networking Industry Association (SNIA). Composed of representatives from all major SAN device manufacturers, various working groups within SNIA are developing standards that will enable the effective interaction between devices and components from different manufacturers. Additionally, some companies that are more actively involved in SAN and Fibre Channel development have taken leadership roles in developing and documenting emerging standards for use by all vendors.

Finally, SAN technology will be more eagerly adopted if it enables solutions to specific storage management problems. One such specific problem facing IT managers today is effective backup & restore. The direct device-to-device communication enabled by SANs makes it possible to provide solutions to this problem that require no server interaction and do not negatively effect LAN performance. Thus, SAN technology will become more widely adopted as a part of the solution to the backup & restore problem.

HP believes that SAN technology and adoption will develop in much the same way as LAN technology. Building on the experience and knowledge gained over the past few years in the development of LAN management solutions, HP is developing SAN management technology in a similar way. Already a leader in LAN management with OpenView Network Node Manager (NNM), HP has leveraged the technology incorporated in NNM for its SAN management product. This approach gives HP customers the advantage of HP's experience in the network management arena and market leadership with other network management tools.

Hewlett Packard’s strategy for developing SAN management solutions is based upon the notion that SANs will be adopted incrementally. Initial applications will likely be in the area of backup and recovery. Examples of early applications of SAN technology are:

• Fibre Channel connection to automated tape libraries enabling the sharing of backup resources among servers
• Host-less or server-less backups
• Multiple/redundant data paths between servers and storage resources in high availability environments

As customers develop familiarity with SANs and Fibre Channel technology, the applications will grow in complexity. Some examples of more sophisticated applications of SAN technology are:

• Dynamic reallocation of storage resources
• Sharing of online storage resources
• SAN management in a heterogeneous environment

As SAN technology is implemented over time, prices will come down on some of the more expensive SAN components and supporting changes will be made to operating systems. Simultaneously, the industry will develop and adopt "de facto" standards for the interaction of components in a SAN environment.

As the initial step in its SAN management product plan, HP announced its first product on May 5, 1999, the SureStore E Storage Node Manager. (Storage Node Manager is a component of the larger SureStore E line of stress-free storage solutions.) Storage Node Manager provides the essential functionality required to manage SANs. Specifically,

• Storage Node Manager automatically discovers devices that are part of the Fibre Channel SAN topology. These devices are mapped in intuitive graphical formats at a central console, providing instant visibility into the SAN. Drill-down, pan & zoom, and other graphical display features are offered to give the user a more detailed view of the SAN. Additional SANs can be remotely monitored from the same central console.

• Storage Node Manager receives device status information from the individual devices and reports it to the central console. Color-coded icons on the SAN map provide instant recognition of devices that experience a status change. In addition, SNMP traps are generated and can be passed on to other management or monitoring applications for action. All events are logged and an event browser can be used to review the event log in detail.

• Storage Node Manager enables the user to easily associate one or more applications with each of the devices in the SAN. With a click of the mouse on the device icon, the user can launch the appropriate management application for that device. Applications can be either server-based or web-based and can be associated with individual devices, groups of devices, specific SANs, or globally defined.

While this initial SAN management product is intended for HP-UX-only environments, HP is already planning to introduce SAN management products for other operating system environments that support a wide variety of Fibre Channel devices.

In parallel with product development for SAN management, HP is taking an active role in working with other Fibre Channel device vendors. Several types of relationships are being developed. First, HP is incorporating support for products from other vendors into HP’s SAN management products by working closely with those Fibre Channel product vendors. Second, HP is developing tight linkages between HP SAN management products and other related software solutions (e.g., network and system management products) by working with those software developers. Finally, HP is taking a leadership role in working with other Fibre Channel product vendors to promote the definition and adoption of common, standard interfaces.

To encourage the early adoption of SAN technology, HP is providing SAN-based solutions to the backup & restore problem. By integrating OpenView OmniBack II (HP’s market-leading backup & restore solution) with other storage management products, customers are able to significantly improve the performance and reliability of this critical function. These integrated products will enable the realization of some of the promising features of SAN technology, such as the automatic initiation of direct disc-to-tape backups with no negative effect on server or LAN performance.

As storage area networks continue to develop and become more widely implemented, it is logical to assume that SANs will evolve in much the same way that LANs have evolved over the past few years. HP’s decision to base its SAN management product on the market-proven technology embodied in OpenView’s Network Node Manager provides the unique advantages of existing technology and a vision for future development. Furthermore, the introduction of SureStore E Storage Node Manager in conjunction with the broader SureStore E line of stress-free storage solutions demonstrates HP’s commitment to take a leadership role in the development of storage area network technology. Finally, by developing working relationships with a wide variety of partners and by actively promoting the adoption of standard interfaces, HP is demonstrating its commitment to the continuing development of its SAN management product line in a way that supports the growth and development of SAN technology in the overall marketplace.