All too often, IT managers are put into a corner when faced with a potential supplier who hits them with the marketing pitch of buying their product or of losing data.

The storage area network (San) arena has seen this approach being doled out in spades. Vendors of servers, Raid products, and fibre channel (FC) switches have tried to force IT managers' hands in choosing between network attached storage (Nas) or a San.

IT managers have seen through this, however, and are continuing to keep a tight rein on their budgets. They are using whatever storage technology makes the most sense in any given part of the enterprise.

Sometimes, it's a matter of reacting promptly to a pressing requirement, driven in turn by storage intensive applications that won't wait for a feasibility study. Pragmatism is the order of the day as IT managers are implementing Sans and Nas in the same enterprise.

Storage purchases, already on a steep growth curve, are projected to continue on that same trajectory for the next few years. It's a sizeable piece of the IT budget and is growing annually.

Storage currently costs about 10p per megabyte, but in three years this could fall to as little as 1p. But despite the fall in cost, storage overall is a large part of the budget as demand for it increases.

Market analysts point to a number of factors driving the voracious consumption of storage. In the age of extranets and intranets, data must be more accessible to parties inside and outside the business, requiring high availability thresholds and fast processing speeds.

Additionally, product catalogues with pictures or sound, or streaming video for training purposes, wolf down megabytes of storage. And IT executives are increasingly curious about how users browse their sites, where they go, what they look at and how much they buy. This customer data has to be stored somewhere.

Nas uses storage servers that connect directly to a local area network (Lan) via TCP/IP and ethernet. Nas works well if a company has large numbers of Lan users, with lots of client-server applications and data getting passed around. The result is that Nas, Lan and data traffic share the same path.

With most Nas appliances all you have to do is plug the hardware into the network and switch it on. If you run out of space, it's just a matter of plugging in another Nas box.

Simple management
Very little configuration or maintenance is required, with management nearly always facilitated using a simple browser interface. Most Nas devices can also be used on mixed platform networks, with the built-in server software supporting access from a range of platforms as standard.

Furthermore, if users change frequently, and there are large numbers of files and projects, Nas may be the best way forward. It also supports multiple operating systems - no small thing when Windows, Unix, Linux and others have to be accommodated. By attaching storage to the network, upgrades are easily handled and management is simplified - or so the argument goes.

In contrast, Sans are separate entities from the other parts of an enterprise network. Using combinations of switches, cabling, disk files, tape libraries and dedicated storage servers, Sans isolate storage traffic from other data flows.

FC, and in some cases gigabit ethernet, ensure that large volumes of data are easily transported across the San. FC transport extends nearly 20 miles - a huge performance edge over SCSI or other host interconnections.

A San is also able to provide a dedicated, high bandwidth data path which is separate from other Lan traffic. Performance is compromised with Nas and you don't get the distance benefits that FC can provide, but there are advantages.

Back-ups are completed quicker and can be run during peak hours on a San without impacting Lan performance. Storage is also easier to share and maintain, with servers running a variety of operating systems which are potentially able to access any San device directly.

The storage can also be located at a distance, with FC Sans able to span many kilometres. This is compared to just a few metres with a server attached to storage devices with SCSI.

FC-based Sans have been around for a number of years, with products on offer from the likes of Compaq, EMC and IBM. Traditionally, each supplier has assumed that customers will only be using its own hardware.

This means that the management software supplied is nearly always specific, both to the hardware concerned and the favoured platforms and management environments of that manufacturer. However, this is all about to change, with more open solutions being promised as customers start to seriously buy into the San concept and build large, multiple vendor Sans.

Like any other network, Sans must be managed. One way of doing this is to use the Simple Network Management Protocol (SNMP). However, while management using the same network for business and information is usual on a Lan, it isn't appropriate for a San. This is partly because the link carrying server-to-storage traffic is probably the busiest on the network and extra overheads can't be tolerated.

Of course, FC vendors must provide suitably feature-rich management information base extensions before the San can be managed from standard SNMP tools and management suites. Much day-to-day management will be reactive: that is, it will respond to a problem that's already occurred.

Problems with FC management may need special skills. Unlike token ring, an FC data frame is removed from the loop after it arrives at its destination. This means that problems may not be visible from all nodes, and it may be necessary to run data-analysers on either side of every suspect port. But this sort of approach is time consuming and may actually impact the fault condition, so look out for Sans with tools to assist with detecting problems quickly.

Mix and match
Theoretically, Sans should offer the ability to mix and match servers, applications, management tools and data switches. But since most vendors opt to protect their revenue base and not push for open standards, most attempts by users to build Sans from multiple vendors end in failure, despite the best efforts from the industry to reach interoperability.

There are several issues that need to be tackled to make Sans more interoperable and easier to manage.

San standards are being developed by a number of organisations including the ANSI T11 committee, which has principal responsibility for FC standards. Elsewhere, the Internet Engineering Task Force and the Storage Networking Industry Association are attempting to resolve storage-related issues, including that of San management.

Unfortunately, there isn't total agreement on the use of FC as there is for Sans. Some argue that the latter is too complicated and expensive, but proponents counter this by highlighting issues relating to the high latency of IP with FC technology designed to support the secure transfer of high volumes of data with minimal latency.

Fortunately, such arguments may soon become a thing of the past thanks to the announcement of a joint technology agreement between Cisco and Brocade. This will see IP and FC technologies used together to extend Sans over wide area network links and the internet.

Under the agreement, FC will be used to build Sans, with Brocade helping to develop FC interfaces for Cisco routers to allow FC-based Sans to be linked together using IP. The latency of IP means this won't allow time-critical storage access over the internet, but it will allow data to be replicated and backed up over large distances. It's a big step forward.

Brocade has applied to the American National Standards Institute, offering to give up the rights to its routing protocol in exchange for an official industry standard. If this request is accepted, the San industry would suddenly open up, ensuring compatibility between multiple vendor equipment. This will give more administrators the confidence to deploy fully-fledged Sans.

According to analyst firm Gartner, the San market will be worth more than £19bn by 2002, so the longer Brocade remains the de facto standard, the stronger and more powerful it will become.

Giving up that standard is probably the only defence Brocade has against being swallowed up by one of its equipment manufacturer customers.

It is thought that if Brocade was owned or even part-owned by a manufacturer partner, the San market would be thrown into disarray and the search for an industry standard would probably have to start again from scratch.

Still, pragmatism is the byword as enterprises in different industry sectors come to grips with strategic objectives and technical requirements. IT buyers of storage are less interested in uniformity across their enterprise than they are in retaining options for growth and management.