Fibre Channel solves storage problems
A review of storage area network basics and a look at technologies that still need development.
Many organizations that have rolled out client-server infrastructures now have multiple islands of computing. While a local area network (LAN) connects each of the islands and its related storage, direct access to that storage is not always possible. Moreover, this type of infrastructure is expensive, inefficient (duplicate resources), and difficult to manage. And it is almost impossible to enforce standard policies.
As corporate capacities increase, driven by data-intensive applications such as multi- media, data warehousing, and ERP, the problem only worsens. Organizations are routinely storing terabytes of information in inflexible structures that provide poor security and system reliability; do not scale easily; and perhaps most importantly do not make data freely available when it is needed.
At the same time, the SCSI channels that connect servers to storage are nearing the end of their useful lives. Limited distance and device connectivity and a typical maximum bandwidth of 40MBps (with Ultra Wide SCSI) are all technology restraints.
The good news is that the storage industry recognizes these problems. A solution is available and is already being adopted for use in mission-critical applications. The enabling technology is Fibre Channel, and the architecture is a storage area network (SAN).
Fibre Channel is a gigabit interconnect technology that combines the best features of channels (high speed and reliability, low latency, and the use of SCSI commands) with those of networks (serial data transmission, many addresses, extended distances, shared services, and scalability). It can also operate as a generic transport mechanism. Fibre Channel is defined in a family of ANSI standards and profiles produced by the X3T11 committee.
Loops and switched fabrics
At its simplest, Fibre Channel provides a point-to-point connection between two nodes. It can also be configured as a loop connecting up to 127 ports, usually through a hub or cascaded hubs and through dual loops for additional fault tolerance. Fibre Channel can also be configured as a switched fabric, in which one or more switches provide multiple one-to-one connections between as many as 16 million nodes. Switched fabrics open the doors to solving today`s storage problems because they enable the development of enterprise SANs.
The simplest SAN enables two servers to share the same storage system. In a more effective SAN, two servers can access two storage systems and share backup. While the primary role of each storage system is to support the applications running on one server, the other server can also access this data when needed without using the LAN. Direct communication between the storage systems makes it easy to enhance data movements over the enterprise network such as for disaster recovery and backup/restore purposes.
The ideal SAN extends this model across the enterprise, providing access to any data, wherever it is located, to any computer. The only additional element needed when a SAN begins to scale is network management functionality. While this is still an ideal, it is well on its way to becoming reality.
Today, a SAN is most easily implemented in a homogeneous environment, in which a single operating system and data structure is already in use. Heterogeneous environments pose a number of difficulties, although a variety of software vendors provide data-sharing capabilities across SANs. Examples include DataDirect Networks, Mercury Computer, MountainGate, and Transoft Networks, which was acquired by Hewlett-Packard earlier this year. (For more information on these software packages, see InfoStor, August Special Report, pp. 14-19.)
Regarding the future of data sharing, there are encouraging developments in common file system software. For example, Veritas Software is developing a distributed file system for Windows NT and Unix. This highlights the importance of a common data access method for open systems. Other efforts include work to define a common disk descriptor, which would allow any system to understand the contents of a disk drive, and the development of object-oriented devices to allow better flexibility with data management and storage resources allocation. Although work in these areas has already begun, widespread acceptance may be two or three years away.
Also, work is underway to improve the functionality of SANs, including backup tools that don`t use the LAN. A few LAN-free backup software products are available today, from vendors such as Legato and Veritas, but as yet there are no global LAN-free and server-free backup solutions for all open-system and SAN platforms. (For more information on LAN-free backup, see InfoStor, September Special Report, pp. 16-20.)
With the addition of tools such as SAN-to-LAN/WAN gateways and associated management modules, the SAN can become a SWAN (storage wide area network) and it can scale up to the answer the needs to large corporations. Again, there are still many challenges that need to be resolved before SWANs will become widely accepted. For example, is ATM, with its concept of "acceptable loss rate," the right choice for a SWAN, or is SONET better?
Although SAN equipment vendors have started to deliver some SAN management tools, global network management tools for SANs are still under development, and again there are debates about the most appropriate tools from the existing traditional network management systems.
The Storage Networking Industry Association (www.snia.org) is currently working on a SAN management standard (based on the CIM model) to enable management software developers to build standardized applications.
Another positive development is the forthcoming arrival of Fibre Channel applications that take advantage of protocols other than SCSI, such as IP today and, later, VI.
All this activity and debate is the mark of a healthy development environment. While many of these areas will not be finalized for several months, they are all being designed to build on existing standards. Any standards-compliant Fibre Channel products in use today will continue to be valid in future SANs. Fibre Channel provides a route that allows IT managers to evolve an efficient, scalable, and manageable storage strategy.
Fibre Channel can be configured in a loop via hubs, or in a fabric with switches.
A SAN enables two servers to access two storage systems and share backup.
Vincent Franceschini is product manager of SAN and high-availability solutions at Hitachi Data Systems Europe (www.hds.com./ www.fibrechannel.com) and director of the Fibre Channel Association, Europe.